Dawn, on the southeastern coast of England, in the year 1011. It is early September, overcast and chill in the last minutes before the sun is up. The farmer standing with his cattle in the field near the River Stour cannot be sure what he sees in the distance, where the river widens to join Pegwell Bay. He looks again. A plume of mist? No -- a sail. A square sail. Viking raiders. The farmer has heard of these people -- raging, half-mad warriors who roar like beasts, who rape women and steal livestock and impale babies on their spears for sport.

The fear is a flash of heat that sweeps down his body, except that suddenly his hands and feet are icy and his legs will not move. The boats, three of them, enter the mouth of the river -- amazing, how well they maneuver in water so shallow -- and rest on the river bank. The Danes are already swarming over the sides, armed with spears and axes, moving swiftly toward the village and its stores of corn and wheat, where, among others, the farmer's wife and infant son sit by the fire, ignorant of the terror that is about to visit. But first it visits the stricken farmer, whose legs have begun to move but not fast enough, whose last earthly vision is that of a bearded man bellowing incoherently and wielding something heavy, and then --

A World of Fear

At the beginning of the last millennium, few people anywhere expected life to be pleasant; pleasure was for the next world, if you made it into Paradise, which was by no means a sure thing. People labored, drank what we would consider to be enormous quantities of alcohol, laughed less than now, believed in malevolent spirits and knew always, with a certainty born of experience, that death could come at any time.

It could arrive swiftly, at the hands of barbarians, or silently in the night, in the form of a raging fever and bright red pustules on the face (smallpox, which afflicted millions and was frequently fatal). It could announce itself as a rattling in the lungs (a sign of either pneumonia or tuberculosis, both fatal), or with the creeping dementia caused by advanced syphilis, which was thought to have been transmitted by demons. Death attended every birth: Puerperal fever, a raging bacterial infection in the mother caused by midwives who delivered babies with dirty hands, killed roughly one woman in eight.

There were means of relief from these ills, but they were uncertain. In Europe, one could wear around one's neck a prayer scrawled on paper, or take a piece of the afflicted person's clothing and bury it. In northern Africa, one could bathe a religious icon in cool water to bring down the fever of the ague; in India, it was known that yellow fever seeks its own color and would leap out of the body of a sufferer into a canary kept close by the bed. People's fears were real, and surreal. Witches could visit a crib at night and suck the breath from a baby, or take possession of people in their dreams, luring God-fearing men into pacts with Satan during unguarded moments of carnal ecstasy. But that was nothing compared with the real fear: the coming of the Antichrist.

The Antichrist was a herald of the Last Days, which everyone in the Christian world believed to be the here and now. He was something between a dragon and serpent, a demoniacal monster who dwelt in the depths of the earth but who could also, on occasion, fly -- a powerful embodiment of chaos and destruction. Descriptions varied, but could be quite precise: Saint Hildegard of Bingen in the 12th century saw him in a vision as a beast with a huge, coal-black head, flaming eyes, ass's ears and an iron-fanged maw. His appearance would be a precursor of the Second Coming of Christ, in which the deeds of every man would be weighed and judged, and those found wanting were to be condemned to an eternal, fiery Hell. The signs, foretold by Jewish and Christian prophets since the 1st century, were all there: war, civil strife, famine, drought, plagues, the deaths of strong rulers and portents in the heavens, such as shooting stars and comets. Especially comets. You didn't have to be a Christian to know that comets were a sign of something evil.

So it was that in April of 1066, in lands from Greenland to Korea, the farm wife closing her stable doors at night or the traveler hurrying to reach his destination by nightfall looked up at sunset and saw something ghastly in the southwestern sky: a brilliant longhaired star, its tail rising like smoke from the horizon almost halfway to the zenith.

Almost no one alive had ever seen anything quite like this one -- not even in China, home to the most sophisticated astronomers in the civilized world. Scholars there went to the books to determine which of the 29 known varieties of comet it most closely resembled, in order to determine exactly what kind of disaster it portended -- whether the death of kings, revolt in the army or famine. They measured the length of its tail to calculate how long the disaster would last. In the monasteries of Europe, it was instantly understood to be one of the 15 signs preceding Judgment Day -- a signal that the apocalypse was at last clearly about to begin, that the crystal orb that contained the world had already fractured. There it was: you could see the spidering crack. Who knew what terrors lay outside?

It was Halley's comet.

When next it returned, 76 years later, people cringed in terror again.

And the next time.

And the time after that. And on and on, into the dawn of the 20th century, when some astronomers calculated that it would finally strike the Earth. So precise were their measurements that they predicted the point of impact to be somewhere between Boston and Boise, incinerating the world in a cloud of cyanogen gas.

Where Fear Resides

It's a curious dance we do with fear. When there is nothing real to dread, we will often manufacture something. A risk-free environment is stupendously boring. "When I get mellow," Woody Allen said, "I ripen and then I rot."

Humans fear fear, but crave it, too. They want pesticide-free food and bungee jumping; passenger-side air bags and roller coasters; three-point child restraints and slasher movies.

Fear is hard-wired into our brains. At the end of the millennium, in fact, science has pretty much located where fear resides: It's in something called the amygdala, two nickel-size clusters of nerve matter buried deep in the skull, about an inch and a half under the temple. Yale doctors who removed the amygdala from the brains of rats produced an animal that would fearlessly climb over the body of a sedated cat and give its natural predator a friendly nibble on the ear.

In humans, though, there is catch: The amygdala governs not just those primitive fear reactions, but the entire emotional climate of the brain. And our emotions -- including fear and anxiety -- are fused with our ability to learn and remember. Memories trigger emotions, and vice versa. They are inextricable.

Humans are better learners than any other species.

Easily scared, though.

Less to Fear

We have less to be scared of now. In most places on Earth, borders are relatively secure. Hell is still out there but the Enlightenment did much to take the edge off it, giving the Christian world a more cozy and compassionate God and a clearer path to redemption. The Copernican revolution pretty much invalidated Stygian geography: The center of the Earth might well be hot but it was almost certainly corporeal. And in the 11th century the predicted immediacy of the apocalypse gradually slipped away, too, after the millennium launched itself without incident.

The greatest elemental fear that stalks us still -- the fear of early death -- is lessened now; science has discovered a vaccine for smallpox, and antibiotics to kill bacteria, and there is always analgesia to ease the pain of whatever science can't cure. In 1000, in most parts of the world, the average man did not live to see his 50th birthday and women tended to die even younger. In most modern societies, both numbers now are at 70, and climbing.

The final century of the millennium, of course, introduced a threat of annihilation unknown before, extinction at the push of a button, and for a brief period of time, the Earth quaked in fear of this; Americans terrified a generation of grade-schoolers by instructing them how to escape the roaring, rolling firestorm of a 10,000-degree thermonuclear wind by crouching beneath a schoolhouse desk with an inkwell.

But that sort of panic waned, though the threat did not.

It may well be that the rational human being can accommodate a certain amount of fear, and no more. And so he prioritizes his terrors, adjusts them so they approximate a constant drone, a background noise that is unnerving, but tolerable. It is the same way we manage to live in denial of our own certain mortality. We expanded or scale back our fears until they just fill the imperfect vessel in which they are contained.

Our children are vastly healthier today, and yet the idea that one of them might die ranks in most polls as our greatest fear. Was this true in 1500, when peasants had a dozen children in the hopes that four or six would live to adulthood? Could it have been?

Rats!

Probably the most frightening thing that ever happened to the human race began for much of civilization in 1347. It was October. A Genoese trading ship arrived at the harbor of Messina from the Black Sea trading port of Caffa, its entire crew either dead or dying. The men had strange black swellings about the size of an egg in their armpits or groin, which oozed blood. Their skin turned black in splotches from internal bleeding. They coughed and perspired heavily; everything that issued from their bodies -- sweat, urine, excrement, breath -- smelled foul. Within five days, every last one was dead. The bubonic plague had come to Europe.

Nobody called it that, of course. At the time, it was known as the Great Mortality, or simply the Pestilence; the Black Death was a name that would be applied much later, by the survivors. By the time the first plague ship arrived in Messina, there had been rumors of a horrible pestilence in the East for about a year, beginning in China or central Asia and moving westward along the major caravan routes, touching Persia, Syria, Egypt and India.

It struck swiftly; people could, and did, go to bed healthy and die before the night was out. "And I, Angolo di Tura, called the Fat, buried my five children with my own hands, and so did many others likewise," wrote one observer in Siena, where the mortality rate was more than 50 percent. Things happened back then that we see only in horror movies. In 1349, two years after the plague ship put into Messina, a ghost ship with a cargo of wool and a dead crew drifted at sea until it finally ran aground near Bergen, in Norway; the rats swimming ashore brought the plague with them.

Though the death the plague brought came relatively quickly, it was not an easy way to go: first came fever, then delirium, then painful and swollen lymph nodes ("Woe is me of the shilling in the armpit!" went one Welsh lament), and finally massive organ failure, internal bleeding -- or, in the respiratory version, a virulent infection that turned the victim's lungs into bright red foamy mush.

Nobody had the slightest idea of what caused this pestilence, and so the first reaction was mass terror. Afflicted households were simply walled up, the living entombed with the dying. Panic took strange forms. People danced in the street, hoping that the noise of their music would keep the plague away, which would sometimes announce itself in a telltale rose-colored welt with a darker ring around it. People would surround themselves with aromatic flowers and herbs to disguise the stench of rotting flesh -- hence the macabre origin of the children's rhyme:

Ring around the rosy

Pockets full of posy

Ashes, ashes

All fall down.

Observers of the time, many of whom recorded what they saw just before succumbing to the plague themselves, wrote of parents deserting their children, and vice versa. Entire towns disappeared.

The first organized reactions to the plague illustrate a primal human response to fear: the attempt to exert control. So we have the Brotherhood of the Flagellants, an underground movement that had been around for two centuries, more or less, but gained immense popularity as a result of the plague. Starting in Hungary in 1348, bands of anywhere from 50 to 500 men would take to the roads, visiting towns and villages along the way. There they would find the local church, strip off their clothes and proceed to beat themselves with leather scourges and iron spikes until they were swollen, bloody masses of black-and-blue flesh -- all in the hope of diverting the chastisement of an angry God, thus keeping the plague away.

The plague killed roughly 20 million people during the 14th century and then retreated to pockets of urban neighborhoods, never entirely going away. There was still no cure. It remained a threat for centuries, still seizing its victims and killing them grotesquely. But that sense of habituation kicked in. It became part of that background noise, that constant drone.

In August 1665, Samuel Pepys's diary records that he had had a particularly erotic dream the night before, and that, oh by the way, he nearly stumbled over the corpse of a plague victim in an alley coming home that night. It gave him quite a start.

"I shall beware of being late abroad again," he writes.

The Big Bad Bug

Through the millennium, we have moved steadily from superstition to science, from rule by fear to rule by reason. And if we remain a fearful people, we tell ourselves that our fears are rational ones now, proportional to the threats. We no longer scan the skies for comets, and kneel in terror to meet our maker.

Check your watch. What time is it?

How many hours before midnight?

You are reading this on a day that some believe, and many fear, will be the last day of life as we know it. Technology collides with theology at the moment of the millennium, a coincidence too compelling to pass unnoticed. Apocalyptic scenarios abound: international monetary crisis, domestic unrest, airplanes falling from the sky. In most doomsday scenarios there is an element of irony and retribution: The secular see a global comeuppance for a world gone mad with technology. Others see a new world order, chaos foretold in the Book of Revelation, on the strangely compelling belief that God counts in base 10 and is attracted to big, round numbers.

Have you stocked up on canned foods and bottled water? Have you hoarded cash? Have you, as many have, installed a portable generator in your home? Bought a gun? Moved to the woods? Built a bunker?

How bad do you think it will be, this Y2K bug?

A mosquito?

A hornet?

A beast with a huge, coal-black head, flaming eyes, ass's ears and an iron-fanged maw?