Header Oikoumene jpeg


Around the shores of the Mediterranean, the early years of the first century AD were an era of unparalleled peace and prosperity for the human race. The Roman Empire looked set to extend itself over most of the known world. However, the territory known to Rome was only a small part of the world as a whole, and the scholars of the Empire were well aware of this.

The world was round, of course. This had been known since at least the time of Pythagoras, five hundred years earlier, and savants such as Pliny the Elder were scornful of those unable to grasp this elementary fact. He said of the Earth as a sphere, "Science and the opinion of the mob are in direct opposition." Science says that the whole Earth is inhabited by men whose feet point toward each other while all have the sky above their heads. "But the mob says how men at the antipodes do not fall off; as though that did not present the opposite query why they should not wonder at our not falling off."

But was the rest of the world inhabited? Learned opinion considered the answer to be yes. The Spaniard Pomponius Mela, about AD 40, said that the Earth was a sphere, a water world comprised of five zones. The equatorial zone was uninhabitable because of heat, and the two polar zones were too cold for life. In the southern temperate zone lived the Antichthones. The land in the northern temperate zone was completely surrounded by the world-ocean, and consisted of the continents Europe, Africa and Asia. The people of the northern hemisphere and the Antichthones could never meet, for even if there were ships capable of navigating the world-ocean, it would be impossible for them to cross the intolerable heat of the torrid zone.

The extent of the world-ocean was a matter for dispute; but geographers agreed that most of the planet was covered by water. Eratosthenes, (b. 276 BC) the first person to measure the size of the Earth, said that the whole world was water except for the three continents of the northern hemisphere, and they occupied only about one-third of that. The inhabited world was about 78,000 stadia in length, and 38,000 stadia wide. The circumference of the Earth at the parallel of Rhodes was 200,000 stadia, at the equator 250,000 stadia. (One stadium was approximately equal to 150 metres). Obviously there would have been little purpose in exploring such an endless world of water, even if there were ships able to do it; but Eratosthenes did say, "If it were not for the vast extent of the Atlantic one might sail from Spain to India along the same parallel."

Crates Globe

Crates of Malles, about 150 BC, disagreed with Eratosthenes. He made a globe of the Earth, which was at least 10 feet in diameter, to illustrate his ideas. He also thought that most of the world was ocean, but said that it held four islands of continental size, two in the northern and two in the southern hemisphere. The known world of the northern hemisphere was the Oikoumene, with the Perioikoi on the other side of the northern globe. The two inhabited areas of the southern hemisphere were the Antipodes and the Antoikoi. The two islands of each hemisphere might be able to contact one another, but the northern hemisphere would be forever separated from the southern by the unendurable heat of the equatorial ocean.

The geographer Strabo (c. AD 19) also believed that there might be unknown continents in the world-ocean inhabited by other races of men. He was surprised at the comparative smallness of the Oikoumene, which was not more than one-third of the total circumference of the globe in the temperate zone. Strabo reduced the width of the inhabited world to 30,000 stadia, as he did not believe that life could exist north of the Arctic Circle. He said that Ireland, the most northerly inhabited kingdom, "not only lies beyond Britain but is such a wretched place to live on account of the cold that the regions on beyond are regarded as uninhabitable." Strabo knew that the Greek explorer Pytheas of Massalia, about 320 BC, had reported that the Atlantic coasts of Europe were inhabited at high latitudes, but considered him a liar; it was well known that the interior of Europe north of the Black Sea was almost intolerably cold. The easternmost boundary of the inhabited world was the Silk Land, where the Stone Tower stood near the shores of an unknown ocean. In the ultimate west were the Islands of the Blessed, last inhabited outposts in the midst of the same sea; the World-Ocean, Earth's greatest natural feature.

Strabo map
The inhabited world according to Strabo (c. 63 BC – AD 19). Strabo said that the length of the inhabited world was not more than one-third of the total circumference of the globe in the temperate zone. In the unknown regions of the world there might be other continents inhabited by human beings.


There might be other inhabited worlds somewhere in Ocean, as Plato, Aristotle, Crates and others believed; but they would never be contacted. Aristotle said that the known world could not be extended by exploration because of excessive heat or cold; while between India and the Straits of Gibraltar, "it is the ocean which severs the habitable land and prevents it forming a continuous belt round the globe." Quite possibly there were no other habitable lands; all was Ocean, except for the Oikoumene.

The Earth was round; so the Moon, also round, might be a world like the Earth. There were some who disagreed; the Moon, being part of the heavens, must be a 'star’ or self-luminous. They pointed out that when the Moon was eclipsed and deep in the Earth's shadow, it did not disappear but glowed with an ashy or reddish light. Clearchus, a disciple of Aristotle, said that the Moon was not a solid body, but “a mere mixture of air and mild fire, that the air grows dark on its surface, as a ripple courses over a calm sea, and so the appearance of a face is produced." Plutarch, the Greek historian who wrote a text
On the Face which appears in the Orb of the Moon some time after AD 71, did not think much of this idea. "It is a slap in the face to the Moon when they fill her with smuts and blacks, addressing her in one breath as Artemis and Athena, and in the very same describing a caked compound of murky air and charcoal fire, a nondescript body smoking and charred..." Plutarch believed the Moon to be "an earth, and that this her visible face, just like our Earth with its great gulfs, is folded back into great depths and clefts containing water or murky air."

Hipparchus (c. 190 - c. 120 BC), the most dedicated ancient astronomer, measured the distance between the Earth and the Moon as 59 Earth-diameters, and the Egyptians considered the Moon's bulk to be one two-and-seventieth part of the Earth's. Plutarch does not say how the Egyptians arrived at this figure; but Aristarchus of Samos (310 - 230 BC), from observations of the curvature of the Earth's shadow on the Moon during a lunar eclipse, had deduced that the Earth was about three times the size of the Moon.

Far beyond the Earth and the Moon, and much larger, was the Sun. Aristarchus had attempted to calculate the Sun's distance from observations of the Moon in its half phase. He estimated that the Sun was about three million miles from the Earth. He knew that this figure could only be an approximation, but he proved that the Sun was undoubtedly much further away, and much larger, than the Moon. Although it appeared to be the same size as the Moon in the sky, the Sun's enormous distance showed that it must be a globe of vast dimensions. It was at least twenty times larger than the Moon, and therefore at least six times larger than the Earth.

What was the Sun made of? Simplistic ideas that it was a ball of fire or a globe of red-hot iron had long since been abandoned. Aristotle believed that the Sun and the stars were composed of the divine fifth element, ether. This element, being unalterable and passive, could not burn. As the Sun and the stars moved through the air, they heated it, and the air, which is the element closest in nature to fire, glowed and burst into flame.


Most philosophers believed that the Earth was at the centre of the universe, but the Pythagoreans disagreed. They said that the central point of the universe was occupied by fire, which they called the "watch-tower of Zeus". They considered fire to be a nobler element than earth, so fire must occupy the central place. The Earth was one of the stars travelling in a circle around the centre. A 'counter-Earth" inside the Earth's orbit was conveniently placed so as to hide the central fire from the Earth's inhabitants. Aristotle dismissed these ideas, especially that of the counter-Earth, as obvious contrivances, "not seeking accounts and explanations in conformity with the appearances, but trying by violence to bring the appearances into line with accounts and opinions of their own."

For Aristotle, the Earth was at rest in the centre of the universe. As the natural motions of the Earth's parts are towards the centre of the Earth, then the natural motion of the Earth itself must be towards the centre of the universe. Travelling outwards from the Earth, were such a thing possible, one would first come to the Moon, then the planets Mercury and Venus, then the Sun, then the outer planets Mars, Jupiter and Saturn. All these bodies were attached to invisible propelling spheres, which moved at varying speeds round the Earth. Beyond the sphere of Saturn, at a vast but unknown distance, was the sphere of the fixed stars. Beyond the stars was the sphere of divine force, the primum mobile which was the ultimate edge of the universe. This was Aristotle's concept; other philosophers disagreed.

However, the universe was recalcitrant. The planets would not move in the perfect circles which theory demanded. Sometimes they seemed to halt in their paths across the sky, move retrograde, and then return to their original course. The planet Mars grew brighter and dimmer, as if it were approaching and withdrawing from the Earth. There were comets and shooting stars; and on Earth there were storms, earthquakes and volcanic outbursts.

Stranger things sometimes happened. In 467 BC, a stone "as big as a wain-load, carrying a burnt colour" fell out of the sky in Thrace, near the River Aegos, and remained where it fell for centuries. The northern sky burned at night with a light like blood as King Philip of Macedonia terrified all Greece, 350 BC. In 86 BC, a "burning shield ran sparkling from west to east" at sunset. The proconsul Licinius Syllanus and his attendants, one night in 66 BC, observed "a spark to fall from a star: and as it approached the earth it waxed greater, and after it came to the bigness of the Moon, it shone out and gave light as in a cloudy day: then, being retired again into the sky, it became a burning lamp." Not only stones and sparks have fallen from the sky, according to Pliny; he mentions falls of sponge-like iron, milk and blood, flesh, wool, tiles and bricks.


In AD 2, stones fell in China, and on November 23 of that year, Chinese astronomers observed a total eclipse of the Sun from Ch'ang-an. The stones were, presumably, meteorites; although we should be wary of stating this categorically. As Pliny the Elder discovered, not only water falls from the sky. Ignoring for the moment falls of organic matter, living and non-living, we find that stones, ice, dust and mud have often been reported to fall from the sky. The stones are usually meteorites. If a stone of non-meteoritic material is alleged to have fallen from the sky, it is usually denied that it fell at all; but even the authoritative Catalogue of Meteorites accepts some falls of non-meteoritic objects as being too well attested to ignore. The "pumiceous glassy object" that fell at Igast, Latvia, in 1855, accompanied by detonations, is accepted, as is the Swedish meteor of 1925, which is said to have dropped fragments of white porous limestone; also the copper meteorite which fell in Colorado, 1931.

On occasion, however, stones of undoubted terrestrial origin do fall from the sky. Also in Sweden, in 1883, filbert-sized stones fell enveloped in large ovoid hailstones. A stone weighing over twelve pounds, composed of a "hard ferrugineous quartzite" fell during a violent thunderstorm at Casterton in Westmoreland, killing a sheep. Most terrestrial stones fall during thunderstorms. Some powerful extension of a thundercloud picked up the Swedish stones and carried them to a great height inside the storm, where they became the kernels of hailstones. A similar agent took up the Casterton stone, but it was too heavy to be lifted to the freezing level. Thus a stone falling from the sky may not be a meteorite.

There was another fall in AD 4, according to Dr. Thomas Short; a rain of blood in London which lasted for five hours. Here the mystery is not in the fall, which, if it ever actually happened, was probably rain contaminated by dust from the Sahara Desert, but where Dr. Short unearthed this historical nugget. Who was recording this event in Britain forty years before the Roman invasion? The almost inescapable answer is "no-one", and we are almost sure that this and most of Dr. Short's other early events are spurious. We are almost sure - but not quite.


In AD 5, the Romans were troubled. There were dreadful earthquakes, and the River Tiber overflowed and flooded Rome for seven days. There was a famine, and on March 28, a partial eclipse of the Sun. The cause of solar eclipses was well known, as the historian Dio Cassius explained. "When...the Moon gets in a direct line with the Sun... and passes under its blazing orb, it obscures the rays from that body that extend toward the Earth. To some of the Earth's inhabitants this obscuration lasts for a longer and to others for a shorter time, whereas to still others it does not occur for even the briefest moment." However, this did not prevent eclipses from being portentous.

AD 9 saw the portent of the eclipse fulfilled. Quintilius Varus, the Roman governor of the province of Germany, marched with his legions to quell an uprising. In a dense forest, a violent storm of wind and rain came on. Treetops were torn off and fell among the Romans slipping on the rain-soaked ground, causing great confusion; and in the confusion the enemy attacked. The Romans suffered heavy losses, but pressed on; until a few days later, when another heavy downpour and violent wind assailed them. Varus' men were unable to advance, stand their ground, or even use their weapons. "They could not handle their bows or their javelins with any success, nor, for that matter, their shields, which were thoroughly soaked. Their opponents... being for the most part lightly equipped, and able to approach and retire freely, suffered less from the storm." Varus’ army was cut to pieces; he and his officers killed themselves rather than be captured.

The Emperor Augustus, horrified by the disaster, at first feared that the victorious Germans might march against Gaul, or even Italy. When he learned that they had not even come to the Rhine, "he ceased to be alarmed and paused to consider the matter. For a catastrophe so great and sudden as this...could have been due to nothing else than the wrath of some divinity; moreover, by reason of the portents which occurred both before the defeat and afterwards, he was strongly inclined to suspect some superhuman agency." The Temple of Mars had been struck by lightning; many locusts flew into the city of Rome and were devoured by swallows. The sky to the north, above the home of the victorious enemy, was troubled. Three columns of fire rose beyond the peaks of the Alps; the sky in many places seemed to blaze and was filled with comet-like flames, while spears seemed to dart from the north and fall in the direction of the Roman camps.

These mysterious northern lights had been seen before. The records of Rome described "military spears...seen on fire in the sky late at night" in 502 BC. The indefatigable Aristotle described how sometimes on a clear night, "chasms, trenches and blood-red colours" appeared in the sky. He named these appearances chasmata. He suggested that a vapour rose from the Earth, composed of two kinds of exhalations; one dry and hot from the land, one moist and vaporous from the water. The dry hot exhalation, being the lightest, rose to the nearest sphere of celestial motion, that which propelled the Moon, and there formed a globe of inflammable material surrounding the terrestrial sphere. When conditions were right, part of this material burst into flame when it was heated by the motion of the celestial sphere. The fire could never reach down to the Earth, however, as below the layer of inflammable exhalation was the moist vapour which formed the Earth's atmosphere. When a large area of the dry hot exhalation burst into flame, the northern sky glowed red; when small pockets caught fire, the appearance of lances and swords was produced.

Aristotle spoke of these northern lights in general terms, giving no examples; but the historians Pliny and Livy were more specific. Pliny says that when C. Coelius and Cn. Papyrius were consuls, "out of the firmament at night, there was seen a light... so as the night seemed as light as the day." In 103 BC armies appeared in the sky. "The Amerines and Tudertes saw men in arms in the sky, rushing one against another from east and west; and those of the west were discomfited." Livy, according to Julius Obsequens, describes this appearance as it was seen from Volsinii, as flames rising from the ground which seemed to reach the sky. The northern lights were often seen as opposing armies in the sky. In fact, in later centuries, the process by which aerial armies transformed themselves into aurorae can be followed almost step by step; although not all such armies were aurorae.

In December of AD 13, the alert observers of China noted a comet. Referring to their manuals, they recorded it as a 'broom star' type. In Chinese comet terminology, a 'broom star' was, as might be expected, a comet with a tail, a
hui. A tailless comet was a 'bushy star', a po. By AD 13, the Chinese had been watching comets attentively for over a thousand years, and had recorded at least 60 cometary appearances, or apparitions. The diligent observers recorded the date of each comet's appearance, its type, its motion among the stars, its form, and its period of visibility. Officials then consulted their textbooks to discover what each new comet portended. The Chinese were indifferent to comets as comets; their close observation was directed to the discovery of what, usually unwelcome, change each comet announced. The textbook discovered at Mawangdui in the 1970s (see Prologue) says that a four-tailed comet signifies disease, a three-tailed one a state calamity, and a two-tailed one a "small war". Yen Tsu, in 516 BC, said that a broom star comet was literally like a broom in that it signalled the sweeping away of evil.


In AD 14, according to Dio Cassius, the Romans were once more disturbed by portents. He says, "... the Sun suffered a total eclipse and most of the sky appeared to be on fire; glowing embers fell from it and blood-red comets were seen." The emperor Augustus died on August 19. However, there was no total eclipse of the Sun in AD 14. The four solar eclipses of that year were all partial. It is possible that Dio, who wrote in the third century AD, decided that portents were required before the death of an emperor, and invented these; alternatively, the fiery sky and 'comets' were another appearance of the northern auroral lights; or, perhaps, Dio was describing one of the mysterious solar obscurations which have been recorded at rare intervals throughout history.

Among the prodigies following the assassination of Julius Caesar, 44 BC, Plutarch mentions a dimming of the Sun, whose orb continued pale and dull for a whole year, so that its disc could be seen without dazzlement by the naked eye. Fruits did not ripen properly. Astronomers have said that this is an example of a 'magical', and therefore impossible, solar eclipse; but it seems clear that Plutarch is describing not a solar eclipse but a solar obscuration. Herodotus records how, about 556 BC, a 'cloud' covered the Sun and caused it to disappear completely. He also notes that in the spring of the year 479 BC, as Xerxes was preparing to invade Greece, the Sun suddenly disappeared, "though there were no clouds in sight, but the sky was clear and serene. Day was thus turned into night... While Cleombrotus was fortifying the Isthmus of Corinth...the Sun was suddenly darkened in mid sky." The nearest solar eclipse to this date was an annular, which was central in North Africa on October 2, 479 BC. In Greece this would have been partial, and insufficient to cause darkness.


In Rome, Tiberius became emperor after the death of Augustus. Three legions in Pannonia took the opportunity to mutiny, resolving on "carrying their petitions, or their swords, to the still unstable throne of a new prince". Tiberius sent his son Drusus, with a staff of nobles and two praetorian cohorts, to quell the mutiny. He had little success. At Nauportus, in the early hours of September 26, AD 14, there was an ugly scene by moonlight. After Drusus had vainly appealed for calm, enraged legionaries began to stone Gnaeus Lentulus, a member of his staff, until Drusus' escort closed in and rescued the bleeding victim. Violence was imminent; but some of the angry thousands looked up and saw that a shadow was beginning to creep across the face of the Moon.

Drusus realised that a lunar eclipse was beginning. He knew the cause of such eclipses; the Moon was passing into the shadow of the Earth. The Greek Anaximenes (585 - 528 BC) had stated this to be the cause of lunar eclipses, and had said that the semi-circular shadow cast by the Earth on the Moon was evidence that the Earth was round. However, the mutinous soldiers, "who had no inkling of the reason, took it as an omen of the present state of affairs: the labouring planet was an emblem of their own struggles, and their road would lead them to a happy goal, if her brilliance and purity could be restored to the goddess". They beat gongs and sounded trumpets in an effort to assist the Moon in her struggle, but nothing availed. The shadow slid relentlessly on, and even that part of the Moon still illuminated began to grow smoky and dim. Then clouds came up, and the Moon was lost to view still shrouded.

The mutiny ended. The soldiers, "so pliable to superstition are minds once unbalanced...began to bewail...their crimes from which the face of heaven was averted." Drusus executed ringleaders, promised reforms, and returned to Rome.

This was not the first time military affairs had been influenced by an eclipse of the Moon. In 412 BC, the expedition of Athens to capture Syracuse in Sicily had ended in failure, and the Athenian fleet was ready to retreat, when, on August 27, the Moon was eclipsed. The general Nicias consulted his soothsayers, who told him that he must stay 27 more days, a complete round of the Moon; and he refused to discuss departure until then. Long before the 27 days were past, the Athenian expedition was destroyed.


In AD 15, Rome was shaken by a violent earthquake, and part of the city walls collapsed. According to Dio, "frequent thunderbolts caused wine to leak even from sound vessels"; the River Tiber overflowed a large part of the city after incessant rains. Many buildings and lives were lost as the river subsided. Ateius Capito and Lucius Arruntius were given the task of preventing future floods, and there was a debate in the Senate as to whether the Tiber should be curbed by altering the courses of the rivers which fed it. Deputations from various municipalities complained that if their local rivers were tampered with, they would be the ones to suffer floods. They said, "Nature had made the best provision for the interests of humanity, when she assigned to rivers their proper mouths - their proper courses - their limits as well as their origins." Rivers were also sacred, and the Tiber should not be deprived of the tributary streams that contributed to his majesty. Eventually the motion of Piso, that nothing should be changed, was agreed to.

Also in AD 15, the northern lights returned, in the form of beams of fire falling from the skies. Once more there was war in Germany. Germanicus Caesar crossed the Rhine, low because of an unusual drought, with four legions. Lucius Apronius was left behind to build roads and bridges, as rains and floods were feared on the return. The four legions crossed lakes which in later times would become part of the Zuydersee, wasted the country between the rivers Ems and Lippe, and came at last to the battlefield in the Teutoburgan Forest, where the bones of Varus' army lay unburied. Germanicus interred the remains, fought an inconclusive battle with the Germans, and marched back to the Ems, where he withdrew two legions by ship. The other two legions, under the command of Publius Vitellius, returned along the shores of the Northern Ocean. However, it was now the equinox, "during which the Ocean is always at its wildest". A northerly storm arose, and the sea rose with it, pouring across the flat land in a vastly swollen tide. "Then the whole land became a flood: sea, shore and plain wore a single aspect; and it was impossible to distinguish solid from fluid, deep from shallow." Men staggered against the waves or were drawn under by the surging flood; the drowned bodies of men and animals dashed against the ranks of soldiers struggling up to their breasts or chins in water. "Words and mutual encouragement availed nothing against the deluge: there was no difference between bravery and cowardice, wisdom and folly, circumspection or chance; everything was involved in the same fury of the elements." At last the survivors struggled on to rising ground, where they spent a miserable night. With daylight, the storm tide retreated. Vitellius continued on to the River Hunse, where he and his legions rejoined Germanicus.

In AD 16, the emperor Tiberius renewed the war in Germany. He considered that the Germans' advantages - their forests and swamps, their short summers and early winters - could be circumvented by a seaborne assault. A fleet of a thousand ships assembled in what was then the mouth of the River Rhine. After a storm and sea flood in the year AD 860, this would become the 'old' or 'crooked' Rhine, "little better than a ditch", on which the modern cities of Utrecht and Leyden stand. The Rhine, like most rivers, was sacred; the Germans attributed to its waters the power to distinguish between children born in marriage and otherwise. If a German child thrown into the Rhine swam, it was legitimate.

Tiberius fought two battles with decisive victories; then, in July, he decided to retire to winter quarters. The majority of the legions boarded their thousand ships, and the fleet passed into the Northern Ocean. Then the storm came; drawing its power, as Tacitus explained, from the moist lands of Germany and the chill of the nearby North. A southerly gale scattered the fleet; then the tide changed and began to flow with the wind. Anchors would not hold; animals, baggage and weapons were thrown overboard in vain. Ships sank, or were stranded on uninhabited islands. Others were driven into the empty wastes of the World-Ocean, "a tract so vast and profound that it is believed the last and landless deep." Many soldiers marooned on remote islands died of starvation. Others survived by eating the drowned bodies of horses washed ashore. When the storm abated, crippled vessels began to come in. These were repaired, and sent out to search the islands, where they rescued a large number of survivors. Some ships had been swept over to Britain, and were returned by the petty kings of that land. The crews of the vessels swept into Ocean came back with terrifying tales of their experiences; "furious whirlwinds, unheard-of birds, enigmatic shapes half-human and half-bestial: things seen or things believed in a moment of terror." Encouraged by the rumoured loss of the Roman fleet, the Germans attacked, but were once more defeated. Demoralised, they complained that "the Romans were invincible - proof against every disaster! They had wrecked their fleet, lost their arms; the shores had been littered with the bodies of horses and men; yet they had broken in again, with the same courage, with equal fierceness, and apparently with increased numbers!"


In AD 17, a great earthquake shook Asia Minor, and twelve important cities, among them Temnos, Aegeae, Myrina and Cyme, were destroyed. Tacitus says, "Even the usual resource in these catastrophes, a rush to open ground, was unavailing, as the fugitives were swallowed up in yawning chasms. Accounts are given of huge mountains sinking, of former plains seen heaved aloft, of fires flashing out amid the ruins."
EQ Map
The earthquake zone of A.D. 17

Earthquakes are the most terrible natural phenomena. They are unavoidable, unpredictable, and invisible. Other phenomena evoke wonder and awe as well as terror; the storm and volcano give some warning of impending disaster; but the earthquake assaults its victims with total surprise. In 373 BC, a great earthquake in the Peloponnesus of Greece was accompanied by a seismic sea wave which overwhelmed the city of Helike. After this disaster, the Greeks sought to discover premonitory indications of earthquakes, but nothing found was unequivocal. Pausanius, the geographer of the second century BC, said that earthquakes were preceded by heavy rains, droughts, irregular seasons, the sudden drying up of springs, solar eclipses, storms, meteors, and pestilential vapours rising from the ground. However, none of these signs could be relied upon, and in any case there were no precautions that served, when the strongest buildings could be shattered and even mountains slid down in ruin. For most of history, earthquakes were even more terrible than they are now. No help rushed from outside to stricken cities; the survivors had to rescue themselves with their bare hands. Best not to speak of what might be happening beneath the earth. There could be no way of finding such things out anyway; but one or two students speculated, since they could do nothing else. There is a tendency to be scornful of the earthquake theories of pre-instrumental scientists, but they could only theorise. The workings of the earthquake remained invisible and unseen.

Lucretius (born C. 100 BC) said that as "the plain facts demand that earth should be of the same nature throughout", the depths of the earth must be filled with caverns and hollows, as it was near the surface. Some of these caves were filled with turbulent winds, others with subterranean rivers equally turbulent, carrying in their floods huge fallen boulders. "With these things lodged and embedded in its bowels, the earth above trembles with the shock of tumbling masses where huge caverns down below have collapsed through age. Whole mountains topple down, and sudden tremors started by that violent shock ripple out far and wide." Sometimes the mere surge and backwash of underground waters makes the earth quiver, as do pots when the water they contain slops to and fro.

Lucretius said that other earthquakes were caused by subterranean winds, sometimes hurling themselves against the walls of imprisoning caverns, sometimes bursting out through the surface of the earth to create enormous chasms. Sidon in Syria and Aegium in the Peloponnesus were wrecked by one such earthquake and outburst, possibly in 92 BC. If the underground wind does not break out, it at last dissipates in a maze of caverns, creating only a minor tremor; until the subterranean water and air gather their strength once more. "So through the menaced cities men tremble with a two-edged terror. While they dread the roofs above, they are afraid that the earth may suddenly fling open its caverns below, gaping wide to reveal a yawning chasm which it will fill pell-mell with its own wreckage."



A 19th-century view of a great comet over the River Nile

In AD 18, Germanicus Caesar, nephew of Tiberius, was touring Egypt. He saw all the most notable sights; the Pyramids, the ruins of Thebes, and the famous Lake Moeris, 220 miles in circumference, supposed to have been dug by a king of that name to receive the overflow of the River Nile.

The Nile, the lifeblood of Egypt, was a great mystery. No-one knew anything of its origins far to the south; how it could flow undiminished without a tributary through a thousand miles of rainless desert; or why it should rise in scorching September and pour over Egypt in a fertilising flood. The Nile flood had never failed; had it done so, Egypt would have died in a year. However, its irregularities were sometimes disastrous. Pliny states that the average rise of the Nile is 24 feet. A low rise leaves some localities unwatered, and a high flood delays sowing in the waterlogged ground. Each year when the Nile flood reached its height, floodgates were opened and the land was irrigated; each strip was sown as the flood retreated. The progress of the annual flood was watched with anxiety. A rise of only 18 feet meant famine, and a rise of 19½ feet hunger. "21 feet brings cheerfulness, 22½ feet complete confidence and 24 feet delight." Pliny says that the highest ever recorded rise was one of 27 feet in the principate of Claudius, 41-54 AD, and the lowest 7½ feet in the year of the war of Pharsalus, 48 BC, "as if the river were attempting to avert the murder of Pompey by a sort of portent." Measuring instruments, or Nilometers, were erected at various places to monitor the rise of the river. They were square wells into which the river was admitted as it rose, with a marble column at the centre marked at frequent intervals with the distance from the lowest level. They were used to adjust taxation to accord with a plentiful or adverse season.


A Nilometer

Most students believed that the Nile flood was caused by the Etesian or 'Annual' winds, which blew from the north for about forty days at midsummer, holding back the flow of the river and causing its waters to 'pile up' and spill out over the land. The Etesian winds might also drive rainclouds southwards, until, trapped against unknown mountains near the Nile's unknown source, they let fall their water; or the snows of these unknown mountains, melted by "the liquefying beams of the all-irradiating sun", might pour down to begin the Nile.

Where did the Nile begin? Pliny said that "the sources from which the Nile rises have not been ascertained, proceeding as it does through scorching deserts for an enormously long distance and only having been explored by unarmed investigators, without the wars that have discovered all other countries". The river was believed to originate in Mauretania, a province of Africa, where it formed a stagnant lake called Nilides. The Nile undoubtedly rose higher when heavy rains fell in Mauretania, and King Juba of that country brought a crocodile from Nilides as proof of the lake's existence.

The historian Herodotus, travelling in Egypt about 460 BC, inquired about the sources of the Nile. No-one he met, Egyptian, African or Greek, could tell him anything about the river's origins, except a recorder in the city of Sais, who claimed to have exact knowledge. He said that the Nile rose between two sharp-peaked hills, Crophi and Mophi, near the city of Syene; one half flowed north to Egypt and the other half south to Ethiopia. This fountain of the Nile was unfathomable. Psammetichus king of Egypt had a rope made many thousand fathoms long, but when this was lowered into the spring it could not touch bottom. However, Herodotus suspected that the recorder was telling him a tall story. He travelled to the city of Elephantine, opposite Syene, and made further inquiries. He found that there was knowledge of the Nile for four months' travel beyond Elephantine; "beyond this none has clear knowledge to declare; for all that country is desert, by reason of heat."

Germanicus went on to see one of Egypt's most well-known tourist attractions; the gigantic stone image of Memnon, which made a strange musical sound at sunrise. This statue stands among the ruins of Thebes, about a mile from the west bank of the Nile. It was erected about 1500 BC by the architect Amenhotep, and is actually a statue of the pharaoh Amenophis III. The statue was in a state of ruin during its 'vocal" period, having been truncated by an earthquake in 27 BC., but was still over fifty feet high. The first person to report hearing the sunrise sound was the geographer Strabo, who visited the statue in 20 BC. He said that the sound resembled that made by a slight blow. Pausanias, who heard the sound in AD 130, said it was like the string of a lyre breaking. Another visitor said it was like the sound made by striking brass. As described, the sound seems rather unremarkable, and it was not heard at every sunrise; yet for 200 years hundreds of visitors came to the statue in the hope of hearing the sound. Some made two or three visits before they were successful, and many never heard it at all. The emperor Hadrian heard it three times on separate days in AD 130, but on his wife's visit there was silence, and she was much annoyed in consequence. The sound was unpredictable. Occasionally it came before sunrise, sometimes up to two hours after, and sometimes it was heard twice on the same morning. It must be concluded that the sound had some quality that was indescribable, for many visitors came several times to hear it. The "cry of Memnon" was last reported in AD 196, after which the statue was reconstructed.
The vocal statue of ‘Memnon’ (right)

Several 19th-century investigators amused themselves by devising elaborate mechanisms by which the sound could have been produced artificially; but it seems certain that the ' cry' was a natural phenomenon, which began with the earthquake of 27 BC, and ended when the statue was reconstructed some time after AD 196. Three scientists with Napoleon's Egyptian expedition of 1798 reported hearing similar sounds "like a breaking string" in a Syene granite quarry and a Karnak temple. In their opinion, their sounds were caused by air trapped in a stone crevice escaping when expanded by heat.

The cry of Memnon is not the only mysterious sound in Nature. Alexander von Humboldt reported certain sounds "like the note of an organ" sometimes heard at sunrise on the Orinoco River. There is the 'underground thunder' of Mexico, the 'Barisal Guns' of India, the 'fog-hiccups' of Belgium, and strange sounds emanating from the mountains of Ireland and the ice-cap of Greenland.

Any natural event that is on a human scale must be almost indistinguishable from the constant flow of natural processes, and normally would pass unrecorded. However, in AD 26, one of these insignificant events, 'personal' rather than 'local' in magnitude, influenced a bid for possession of the Roman Empire. Lucius Aelius Sejanus, commander of the Praetorian Guard, ingratiated himself with the emperor Tiberius and resolved to inherit the empire. Having surreptitiously poisoned Tiberius' son Drusus in AD 23, Sejanus had a fortuitous opportunity to gain the emperor's confidence three years later. While they were dining at a villa called the Cave, in a natural cavern between Amyclae and Fundi, there was a fall of rock at the cave mouth which killed several servants. Most of the diners fled. Soldiers rushed to the rescue, and found Sejanus crouched over Tiberius, claiming to have fended off falling rocks from the emperor's person. Tiberius believed his story, and thereafter trusted Sejanus implicitly. Sejanus even persuaded Tiberius to retire to Campania, leaving him as head of the empire; but when Sejanus proclaimed himself Emperor of Rome, it was too much. The ex-favourite of Tiberius was thrown into prison and strangled on the same day in AD 31.


The comet observers of China were not released from duty when dawn came. During the day they continued to watch the skies, directed by officials to look for chien (overshadowings), an (eclipses), meng (daytime obscurities), chi (rainbows) and hsiang (unusual cloud forms). They were particularly instructed to record yun (haloes). The awesome dedication of generations of Chinese observers is shown by the fact that they had seen and described most halo phenomena while Europeans were scarcely aware that such things existed. On May 13, AD 31, they reported that "the Sun appeared with a complete halo (yun) and a partial lateral arc (pao), while a white rainbow penetrated the halo. This was observed 8 degrees from the lunar mansion Pi."

The rainbow, formed by the refraction and reflection of light through water-drops, is famous, because it appears in the sky opposite the Sun, and is thus easy to observe. Haloes, which encircle the Sun (or Moon), and are formed by the refraction and reflection of light through ice-crystals, are much less well-known, as they are not noticeable unless searched for; yet they are much more common than rainbows. The most frequent halo phenomenon is the luminous ring of 22 degrees radius, which can be seen around the Sun or Moon at least once a month. Sometimes it is white, but often it shows subtle spectrum colours, with red nearest the Sun. Almost as common are parhelia, 'mock suns' or 'sun dogs', which appear on one or both sides of the Sun when it is low in the sky. (Their lunar equivalents are parselenae). These are luminous patches, often very bright, with vivid colours, sometimes combined with a halo.

Other halo phenomena are much rarer. There are haloes of various sizes, larger or smaller than the 22-degree circle; multiple parhelia; anthelia or "counter-suns'; and a bewildering variety of arcs and bows which can intersect the luminary, the haloes and the parhelia. Many of these manifestations have only been recorded once; others are theoretically possible, but have never been seen.

Aristotle, of course, observed haloes, parhelia, and some of the arcs; but he was more interested in the rainbow. The subtle, elusive beauty of halo phenomena, however, fascinated the Chinese. By about AD 635, they had recorded and named almost every variation. In the year 1425, the emperor Chu Kao-Chih wrote a textbook on the subject, illustrated with coloured drawings. The Chinese interest in haloes was, as usual, not just aesthetic. Like everything else in the sky they were portents. Prognosticatory officials studied the halo records of the observers in order to determine if they indicated good fortune or ill. For instance, yellow and white parhelia predicted happiness. An army which sees a single parhelion by the side of the Sun will have good luck; when it is seen west of the Sun, the western army will gain victory, and if east of the Sun the eastern army will conquer. In peacetime a parhelion predicts the promotion of a general.

With the Chinese, the science of portents reached its highest development. In Europe, amateurs undertook the interpretation of prodigies, and only the most dramatic events were recorded; in China it was organised and institutionalised to a point where everything that could possibly happen in the sky had its earthly meaning. The jih tai (sun crowns), the chheng fu (glorious supports) and other beauties of the sky also performed a mundane service in China. Once they had foretold the fortunes of the State, they could also be used for predicting the weather.