I found myself trying to recollect the face of Marcus Crassus, the richest man in Rome. I had seen him a hundred times in the Forum, but his visage escaped me. I counted money in my head, imagining the soft jingle of coins in a purse, and spent my fee a dozen times over. I thought of Bethesda; I imagined her sleeping alone with the kitten curled up between her breasts, and I traced a path by memory from room to room through my house in Rome, like an invisible phantom standing guard. Abruptly an image rose unbidden in my mind, of Belbo lying across my portal in a drunken stupor, with the door wide open for any thief or assassin to step inside…

I gave a start and sat upright. Eco turned in his sleep and made a chattering noise. I strapped on my shoes, wrapped the blanket around me like a cloak, and returned to the deck.

Here and there sailors lay huddled together in sleep. A few strolled the deck, watchful and alert for any danger from the sea or shore. A steady breeze blew from the north, filling the sail and raising gooseflesh wherever the blanket did not cover my arms and legs. I strolled once about the deck, then found myself drawn towards the portal amidships that led down into the galley.

It is curious that a man can sail upon many ships in his life and never wonder at the hidden motive power that drives them, yet this is how most people live their lives every day – men eat and dress and go about their business, and never give a thought to all the sweat of all the slaves who laboured to grind the grain and spin the cloth and pave the roads, wondering about these things no more than they wonder about the blood that heats their bodies or the mucus that cradles their brains.

I stepped through the portal and down the steps. Instantly a wave of heat struck my face, warm and stifling like rising steam. I heard the dull, throbbing boom of the drum and the shuffling of many men. I smelled them before I saw them. All the odours that the human body can produce were concentrated in that airless space, rising up like the breath of demons from a sulphurous pit. I took another step downward into a world of living corpses, dunking that the Jaws of Hades could hardly lead to a more terrible netherworld than this.

The place was like a long, narrow cavern. Here and there lamps suspended from the ceiling cast a lurid glow across the pale naked bodies of the oarsmen. At first, in the dimness, I saw only an impression of rippling movements everywhere around me, like the writhing of maggots. As my eyes adjusted I slowly made out the details.

Down the centre ran a narrow aisle, like a suspended bridge. On each side slaves were stationed in tiers, three-deep. Those against the hull were able to sit at their stations, expending the least effort to power their shorter oars. Those in the middle were seated higher and had to brace themselves against a footrest with each backward pull, then rise from their seats to push the oars forward. Those on the aisle were the unlucky ones. They ran the catwalk, shuffling back and forth to push their oars in a great circle, stretching onto their toes at full extension, then kneeling and lurching forward to lift the oars out of the water. Each slave was manacled to his oar by a rusted link of chain around one wrist.

There were hundreds of them packed tightly together, rubbing against one another as they pushed and pulled and strained. I thought of cattle or goats pressed together in a pen, but animals move without purpose. Here each man was like a tiny wheel in a vast, constantly moving machine. The drumbeat drove them.

I turned and saw the drummer at the stern, on a low bench that must have been just below my bed. His legs were spread wide apart. His knees grasped the rim of a low, broad drum. Thongs were wrapped around each hand, and at the end of each thong was a leather ball. One by one he lifted the balls in the air and brought them down upon the skin of the drum, sending out a low pulse that throbbed through the dense, warm air. He sat with his eyes closed and a faint smile on his face as if he were dreaming, but the rhythm never faltered.

Beside him stood another man, dressed like a soldier and holding a long whip in his right hand. He glowered when he saw me, then snapped his whip in the air as if to impress me. The slaves nearest him shuddered and some of them groaned, as if a wave of pain passed over them.

I pressed the blanket over my mouth and nose to filter the stench. Where the lamplight penetrated through the maze of catwalks and manacled feet, I saw that the bilge was awash with a mixture of faeces and urine and vomit and bits of rotting food. How could they bear it? Did they grow used to it over time, the way men grow accustomed to the clasp of manacles? Or did it never cease to nauseate them, just as it sickened me?

There are religious sects in the East which postulate abodes of eternal punishment for the shades of the wicked. Their gods are not content to see a man suffer in this world, but will pursue him with fire and torment into the next. Of this I know nothing, but I do know that if a place of damnation exists here on earth, it is surely within the bowels of a Roman galley, where men are forced to work their bodies to ruination amid the stench of their own sweat and vomit and excreta, playing out their anguish against the maniacal, never-ending pulse of the drum. To become mere fuel, to be consumed, drained and discarded with hardly a thought, is surely as horrible a damnation as any god could contrive.

They say most men die after three or four years in the galleys; the lucky ones die before that. A captive prisoner or a slave guilty of theft, if given the choice, will go to the mines or become a gladiator before he will serve in the galleys. Of all the cruel sentences of death that can be meted out to a man, slavery in the galley is considered by all to be the cruellest. Death comes, but not before the last measure of strength has been squeezed from a man's body and the last of his dignity has been annihilated by suffering and despair.

Men become monsters in the galleys. Some ship captains never rotate the positions of the slaves; a man who rows for day after day, month after month on the same side, especially if he runs the catwalk, develops great muscles on one side of his body out of all proportion to the other. At the same time his flesh grows pale as a fish from lack of sunlight. If such a man escapes, he is easily detected by his deformity. Once in the Subura I saw a troop of private guards dragging such a man from a brothel, naked and screaming. Eco, then only a boy, had been horrified by the slave's appearance, and then, after I had explained it, had begun to weep.

Men become gods in the galley, as well. Crassus, if indeed he was the owner of this ship, took care to rotate his rowers, or else used them up more quickly than most, for I saw no lopsided monsters among them. Instead I saw young men with deep chests and great shoulders and arms, and among them a few older survivors with even more massive physiques, like a crew of bearded Apollos sprinkled with a hoary Hercules here and there, at least from the neck down. Above the neck their faces were all too human, wretched with care and suffering.

As I looked from face to face, most of them averted their eyes, as if my gaze could hurt them as surely as the whipmaster's lash. But a few of them dared to look back at me. I saw eyes dulled by endless labour and monotony; eyes envious of a man who possessed the simple freedom to walk about at will, to wipe the sweat from his face, to clean himself after defecating. In some eyes I saw lurking fear and hatred, and in others a kind of fascination, almost a lust, the kind of naked stare that a starving man might cast on a glutton.

A kind of fever seized me, warm and trancelike, as I walked down the long central aisle between the naked slaves, my nostrils filled with the smell of their flesh, my skin awash in the humid heat of their straining bodies, my eyes roving among the great congregation of suffering constantly asway in the darkness. I was a man in a dream watching other men in a nightmare.