‘Is he your lover?’ I blurted out.

‘I have no lovers, Parmenon. Only men I have to deal with.’

‘And me?’

‘Why, Parmenon, you are my right hand. We are one.’ She glanced towards the door. ‘Go and see what happens to Sejanus and report back to me. Remember what I have said!’

She pushed me out of the room. In the corridor she held me back.

‘You have done well, Parmenon.’ Her voice was excited. ‘You and I are locked together like spokes in a wheel: don’t you understand that?’

A scream echoed up the stairs. One of the soldiers was helping himself to a slave girl.

‘You left me vulnerable,’ I accused.

‘Don’t moan!’ Agrippina’s face turned ugly. ‘Remember the arena. You wanted to enter, so now you must fight or you die. Do what you have to!’ Her face softened. She waggled her fingers, like a little girl saying goodbye, and went back into the room.

The Palatine was now in uproar. Macro, using the Emperor’s warrant, had ringed the entire hill with troops from the Urban Cohort. These had already caught some of Sejanus’s followers who were being led off to the city prisons with bound hands and bloody faces. A few members of Sejanus’s personal bodyguard had attempted resistance, only to die in an untidy, bloody heap in a corner of the square. Macro’s men recognised me and I was let through. I raced up the steps leading to the great enclosure of the Temple of Apollo, where there were more corpses and ever-widening pools of blood. Severed heads already decorated the spikes which fringed the Stairs of Sighs.

In the colonnades I glimpsed the bodies of more victims, strung up from iron torch-holders and left to swing softly in the morning breeze. I reached the temple doors where Macro stood surrounded by his officers.

‘You have been to see Agrippina, haven’t you?’ Macro sneered. ‘Clever and quick as a rat, eh? You should. .’

His words were drowned by a roar from inside the temple. Sejanus, a parody of what he had been, was dragged out, his face bloody, his clothes torn. As he was pushed towards Macro, I saw that his mouth was nothing but a bloody mess: the clicking tongue had been silenced for ever. Macro stared, head to one side, as if he couldn’t really believe what he was seeing.

‘Well, well, Sejanus,’ he sighed. ‘Life is like a game of dice.’

Sejanus’s eyes turned to me with a flicker of recognition. I hardly recognised his bruised and battered face. The hair had been torn from his head, oozing cuts sliced his arms and shoulders, there were even teeth marks where his enemies had bitten him. He opened his mouth in a hideous moan.

‘What’s that?’ Macro asked, leaning forward. ‘You want to see the Emperor? Rome can no longer tolerate such treason.’ His voice rose. ‘Bring him with me!’

Macro gestured at me to follow, in what was supposed to be a triumphant procession across the Palatine to Sejanus’s palace. Macro swaggered in front surrounded by his guards, their shields up and swords drawn. Sejanus, now bound by ropes, was led like a reluctant horse, as the assembled mob hurled abuse at him. Men, women and children pushed and shoved at him, pelting him with rotten food and other missiles, spitting and cursing at the Emperor’s fallen favourite. Our journey became a trail of blood, until even Macro tired of the fun. The guards drove the mob off as we entered the colonnades. We crossed a garden, went down some steps and I found myself in the same torture chamber I’d visited when I had first met Sejanus. The guards were left in the corridor. Macro’s officers, myself included, watched as the prisoner was made to squat on a stool. The executioners stepped forward, their faces covered by ghastly animal masks. A noose was placed round Sejanus’s throat, and a small, steel rod was slipped through the knot, which the executioner slowly turned. I glanced away, as terrible groans and gasps came from the dying man. One of Macro’s men joked about eyes popping out. Sejanus’s feet beat the floor to the jeers and laughter of the onlookers. Once it was over, hooks were fastened to the corpse and it was dragged out along the passageway, through the city and thrown down the Steps of Mourning. The mob were encouraged to tear and pluck at it, so viciously that the executioner had difficulty in finding a piece of flesh big enough to place the hooks in to drag Sejanus’s corpse down to the Tiber.

As the old year gave way to the new, the killings, proscriptions and denunciations gathered pace. It was the age of the informer and spy. Every week Tiberius sent a list from Capri denouncing his enemies, even his friends. Father turned on son, brother against brother. Some men acted nobly. One senator, when accused of being a friend of Sejanus, rose in the Senate and proclaimed.

‘Yes, I was and so was Tiberius. I was proud of being Sejanus’s friend. What treason is there in that?’

His courage and ability saved him. Others were not so fortunate. Agrippina and I became silent observers of the mounting horror. She refused to leave the palace but stayed in her quarters or walked in the garden.

‘Will the Emperor now show mercy to your mother and Drusus?’ I asked.

Agrippina was painting a doll, a gift for the daughter of one of her handmaids.

‘Tiberius never forgets and never forgives. He will compromise. Gaius and his sisters will survive but there will be no mercy shown to the rest.’

She held the doll up, her tongue half-sticking out of her mouth as she painted its face.

‘I’ll keep quiet and hide deep in the shadows.’ She put the brush down and wiped her fingers on a rag. ‘It’s going to be a pretty doll, isn’t it, Parmenon? If I can’t have children at least I can look after those of others.’

‘Why can’t you have children?’

‘You could have taught them grammar, Parmenon. I should have said, won’t.’ Her eyes became fierce and hard. ‘I’ll never have children whilst that monster on Capri lives. Until he’s dead, no one’s safe.’

Agrippina’s prophecy was as shrewd as it was accurate. Apicata, Sejanus’s estranged wife, wrote a letter to Tiberius denouncing her dead husband as the murderer of Tiberius’s son Drusus. She then took a warm bath, opened her veins and escaped the Emperor’s vengeance. The news drove Tiberius to the edge of madness: no possible rival was safe. On Pandateria, Agrippina’s mother was starved to death. Her brother Drusus was never released from prison; he died a starving madman, tearing and eating the stuffing from his own mattress.

More deaths occurred. Tiberius’s old colleague, Sextus Letillus, opened his veins when the Emperor denounced him but promptly closed them, thinking he might escape with a begging letter. When he received Tiberius’s reply, he quickly opened his veins again and announced that he welcomed death. One senator took poison in the Senate, drinking it cheerfully whilst he denounced Tiberius’s cruelty and rapacity. Another senator, Sabinus, was executed and his body exposed on the Steps of Mourning. His faithful dog brought food every day and placed it close to the dead man’s mouth. Even when the corpse was thrown into the Tiber, the animal plunged into the water and kept it afloat before the admiring gaze of the people, who saw it as a clear sign of the dead man’s innocence.

Youth and innocence were no defence. Sejanus’s children went under the knife. His son was old enough to know what was happening, but his young daughter, distraught, kept asking everyone what she had done wrong and where was she being taken? As she was a virgin, the executioner violated the girl immediately before strangling her. Both corpses were exposed to the public view.

I tried to draw Agrippina into conversation about what would happen next but she shook her head. She never mourned her mother or brother: that was too dangerous and could be taken as treason. She grew thinner, paler. She went to bed late and rose early, busying herself with humdrum tasks. I was aware of her tension. Sometimes she would let me embrace her or hold her hand but then she would push me away. Some days she’d disappear and come back red-eyed, with bruises on her arms and legs. I suspected she was visiting Macro, Rome’s new master, and her only link with Tiberius. Days, months and years slid one into the other. If Agrippina kept free of the politics of Rome, she also ensured I did the same. I was never entrusted with any secret tasks or sent on mysterious errands. Instead I became her steward and secretary, kept busy organising stores and purchasing goods. Occasionally I would be sent out to her villa at Antium to check that all was well there.