But Alexander wasn’t done yet. Trumpets pealed out again from the city walls. With a great clang, gates were thrown open, and the Macedonian cavalry at last rode out into the field. Even as they emerged they were in their tight wedge formation. At a glance Josh could see how much more skillful these horsemen of ancient times were than the Mongols. And, at the head of the Companions who rode out from the right-hand side, Josh recognized the bright purple cloak and white-plumed helmet of Alexander himself, a panther skin thrown over his saddle cloth, as ever leading his men to glory or death.

The Macedonians, fast, agile, and tightly disciplined, wheeled to cut into the Mongol flank like a scalpel. The Mongols tried to turn, but, compressed now between the stolid Macedonian infantry and the Companions, their movements were constricted, and the Macedonians began to jab at their unprotected faces with their long wooden spears. It was another classic tactic, Josh knew—a battle formation perfected by Alexander the Great, yet inherited from his father before him, with cavalry on the right delivering the killer blow, and the central infantry following up with its dogged pressure.

Josh was no advocate of war. But he saw a kind of elation in the eyes of warriors on both sides as they hurled themselves into the fray: a kind of release that the moment in which all inhibitions could be shed was here at last, and a sort of joy. Josh felt a deep visceral thrill as he watched this ancient, brilliant maneuver unfold before his eyes—even as men fought and died in the dirt below, each one a unique life snuffed out. This is why we fight wars, we humans, he thought; this is why we play this game with the highest of stakes: not for profit, or power, or territory, but for this intense pleasure. Kipling is right: war is fun. It is the dark secret of our kind.

Perhaps that was why the Eyes were here—to enjoy the unique spectacle of the universe’s most vicious creatures dying in the dirt. Josh felt resentment, and a certain squalid pride.

Save for some reserves, nearly all the forces were in the field now. Apart from a few cavalry skirmishes on the fringe, the battle was concentrating into that tight, bloody mass of carnage at the center of the field, where men lashed at each other relentlessly. Still the fire pits burned, throwing up smoke that obscured the action, and still arrows rained down from the walls of Babylon.

Josh could no longer tell which way the advantage of the battle went. It wasn’t a time for tactics now, and the opposing generals, perhaps the greatest of all time, could do no more—save, like Alexander, to swing swords themselves. It was a time to fight, or die.

Bisesa’s medical station was overwhelmed. There was no other word for it.

Working alone, she struggled to save a Macedonian, sprawled unconscious on the table before her, dumped like a carcass in a butcher’s store. He was a boy, no more than seventeen or eighteen years old. But he had taken a javelin thrust to the stomach. She cleaned, padded and patched the wound as best she could, her hands trembling with fatigue. But she knew that what would finish the boy off was the infection caused by the garbage that spear point would have carried in with it.

And still, all around her, the bodies flowed in. Those selected by the triage teams were no longer carried to the town house she had designated as a morgue but were rudely dumped on the ground, where they were piling up, their dark blood staining the Babylonian dirt. Of those selected for treatment, a handful had been patched up and gone back out to fight, but more than half her patients had died on the treatment tables.

What did you expect, Bisesa? she asked herself. You’re no doctor. Your only experienced assistant is an ancient Greek who once shook hands with Aristotle himself. You’ve no supplies, you’re running out of everything from clean bandages to boiled water.

But she knew she had saved some lives today.

It might be futile—the great wave of Mongol aggression might break over the walls and destroy them all—but, for now, she found she really and truly didn’t want this boy with the punctured stomach to die. She dug into the guiltily hoarded contents of her twenty-first century medical kit. Trying to hide her actions from the others, she jabbed a shot of streptomycin into the boy’s thigh.

Then she called for him to be taken away, like all the others. “Next!”

Kolya believed that the Mongols’ expansion was pathological. It was a ghastly spiral of positive feedback, born of Genghis Khan’s unquestioned military genius and fueled by easy conquests, a plague of insanity and destruction that had spread across most of the known world.

Russians especially had reasons to despise the memory of Genghis Khan. The Mongols had struck twice. Great cities grown fat on trade, Novgorod, Ryazan and Kiev, were reduced to boneyards. In those dread moments the heart had been torn out of the country, forever.

“Not again,” Kolya whispered, unable to hear the words himself. “Not again.” He knew Casey and the others would resist the Mongol menace as hard as they could. Maybe the Mongols had made too many enemies in the old timeline; maybe in some transcendent way they were now facing payback.

Of course his own gamble was still to be played out—was his weapon powerful enough, would it even work? But he had confidence in his own technical abilities.

Reaching the target, though, was another matter. He had observed Genghis. Unlike Alexander, Genghis was a commander who had watched battles from the safety of the rear, and retired to his yurt at the close of the day; aged nearly sixty, he was predictable to that degree.

Could Kolya be sure, though, any longer, after three days, quite what time it was? Could he be sure that the heavy tread he sensed now was indeed the man he sought to destroy? His only real regret was that he would never know.

Kolya smiled, thought of his wife, and closed the trigger. He had no eyes, no ears, but he felt the earth lurch.

Abdikadir was back-to-back with a handful of British and Macedonians, fighting off Mongols who swirled around them, most still on horseback, lashing and cutting. His ammunition long exhausted, he had dropped the useless Kalashnikov and fought with bayonet, scimitar, lance, javelin, whatever came to hand, the detritus of dead warriors from ages separated by more than a thousand years.

As the battle had closed around him, at first he had felt as if he had become more alive—as if his life had been reduced to this instant, of blood, noise, intense effort and pain, and all that had gone before was a mere prologue. But as fatigue poisons built up, that sense of vividness had been replaced by a coppery unreality, as if he was on the point of fainting. He had trained for this—the “drone zone,” they called it, a place where the body ignored pain, grew impervious to hot or cold, and a new form of consciousness cut in, a kind of dogged autopilot. But that didn’t make it any easier to bear.

This little group was surviving where others had already been cut down, an island of resistance in a sea of blood across which the Mongols surged at will. He himself had taken blow after blow. But he knew he couldn’t take much more. The battle was being lost, and there was nothing he could do about it.

Over the carnage of the battlefield, he heard the cry of a trumpet, an uneven rhythm played on a war drum. He was briefly distracted.

A mace swung down from the sky, smashing the scimitar from his hand. Pain lanced; he had broken a finger. Unarmed, one-handed, he turned to face a Mongol cavalryman who reared above him, raising the mace again. Abdikadir lunged, his good hand stretched out stiff as a board, and stabbed at the Mongol’s thigh, aiming for a nerve center. The cavalryman stiffened and flopped backward, and his horse stumbled back. Abdikadir got to his knees, found his scimitar in the bloody dirt, and straightened up, panting hard, looking for his next assailant.