Life inside these thick walls was one of extreme drudgery. Having worked since the age of seven, Romulus was expert at sweeping the kitchen floor, chopping wood for the ovens, unblocking drains and other menial tasks. But much of the time he was bored. Most of his jobs could be finished in just a few hours. To be ordered to the domus of one of Rome's foremost men was a thrilling break in routine.

Gemellus reached into his tunic and pulled out a folded parchment sealed with wax. He frowned, worried that his largest creditor would refuse the plea he had composed.

'Make sure nobody follows you.' The Greeks' thugs had been watching every adult slave for days and they must not discover he owed money to others. 'Understand?'

'Yes, Master.'

'Wait for a reply.' Gemellus dismissed him. 'Be quick!'

Romulus darted into the tablinum, skidding across cool mosaic tiles. He paused just long enough to whisper his news to Fabiola, who had returned to peer into the garden.

She grinned as he tore off again, pleased for her brother.

Exiting the imposing reception room at speed, the boy nearly knocked over Quintus, the old slave who was sweeping round the rectangular pool that collected rainwater in the centre of the sunlit atrium.

'Sorry!'

Quintus smiled fondly. Aware of Gemellus' cruelty, Romulus often helped him when his chores grew too much. The salt mines awaited any in the house who could not work.

Quickly regaining his balance, Romulus pelted towards the heavy wooden doors that guarded Gemellus' house from the outside world.

Juba, the immense doorman, stood up when he saw Romulus approaching. He wore only a loincloth and his muscular body was covered in old scars. A bald head shone from the covering of grease the Nubian applied daily. Attracted by his size and fighting ability, Gemellus had bought Juba five years before. A man like this would keep trouble from the door and other slaves in check.

The Nubian lifted an eyebrow.

Romulus looked round, making sure nobody was within earshot. 'The master gave me a letter.' He blew out both cheeks and waddled closer, impersonating Gemellus. 'For Crassus, the famous general.'

Juba laughed, revealing the stump of his tongue. Gemellus had ordered it cut out when he had purchased the doorman. It meant the Nubian always had to consult his master or the major-domo when someone was outside. This reduced the chance of thieves entering the domus.

Romulus remembered watching with amazement as he walked into the house, still bleeding from the mouth. He was the first black man the boy had seen. And mutilation, poor food and frequent beatings had ensured that Juba hated their owner as much as Romulus did.

Soon after arriving, the Nubian had carved him a wooden sword, delighting the eight-year-old with his first toy. In return Romulus had stolen a loaf of bread from the kitchen. From then on, nightly raids had kept the giant fed. Their friendship had grown from there. Previously, Fabiola had been his only ally. Although the twins were very close, Romulus had unconsciously craved male company, rough and tumble play. He began to seek Juba out every day and, glad of the boy's presence, the Nubian let him share his bare alcove by the door without complaint. Velvinna knew how important the relationship was and did not interfere. Romulus would never have the influence of his father. Or even meet him.

Unless it was to exact revenge.

The rape was something she had always planned to tell Romulus and Fabiola about when they were older. Thanks to his increasing popularity, depictions of a certain noble had recently begun appearing in temples and shrines. Velvinna had seen many examples and was now reasonably sure of the twins' father's identity. She longed to tell them both, especially Romulus. Thirteen years later, the desire for revenge still burned inside her. But it was important that they enjoyed childhood as much as possible – before it was taken away by whatever Gemellus might plan. Mixed feelings filled Velvinna as she saw the merchant gazing speculatively at the children and her prayers to the gods grew more fervent.

Romulus knew none of this. Grinning broadly, he stood before two great portals at the entrance. They were seldom opened, except when important visitors arrived or Gemellus was holding a feast. Instead the inhabitants came and went through a postern gate in the middle of one door.

Throwing back the iron bolt, Juba smiled and held up a stern finger.

'I'll be careful!' Eagerly, Romulus eyed the curved blade shoved into the Nubian's wide leather belt. 'Can we practise again later?'

Juba mimed the cut and thrust of a sword fight.

Grinning broadly, Romulus ducked into the noisy street. A wave of heat hit him, assaulting his senses with its odours. As always in warm weather, the overwhelming smells were of human faeces and urine, fermenting on dung heaps in small dark alleyways.

He wrinkled his nose with disgust.

The narrow unpaved lane was crowded with people going about their business. Rome's working day began at sunrise, especially in summer when the extreme temperatures made life unbearable. The men and women Romulus saw pushing and shoving past were a mixture of every race in the Republic. Italians, Greeks, Spaniards. Nubians, Egyptians, Gauls, Judaeans, even the occasional Goth. Most were ordinary citizens or traders, trying to eke a living in the city designed for, and ruled by, the upper classes.

Many had come here to seek fame and fortune.

Few succeeded.

But their lot was better than those who had arrived as slaves, destined merely to serve as tiny cogs in the huge machine that the Republic had become. Only the rich, born into a heritage stretching back five hundred years, truly enjoyed the splendour of the metropolis and the opportunities it afforded.

A pair of heavily muscled men leaning against a wall opposite stood out, noticeable for their size and stillness. They were watching Gemellus' doorway like hawks. Thick leather wristbands, swords on belts and scarred arms meant only one thing. Trouble.

Juba had pointed them out earlier through a peephole. When Romulus left the villa, one of the heavies hurried after, trying to stay inconspicuous.

The boy increased his pace, smirking at how easy it would be to lose his pursuer. Although he hated Gemellus, Romulus felt a loyalty to the household.

Delivering the message as ordered was important.

Turning a corner without looking, he was nearly run down by a pair of oxen pulling a cart loaded with pottery.

'Mind where you're going, little bastard!' The drover waved a stick angrily, trying to bring his startled beasts under control. Loud crashes signalled breakages as some of the load came loose.

Guiltily, Romulus disappeared into the throng. Shouts of rage followed but neither carter nor thug had a chance of catching him. During the day all traffic moved at snail's pace through the packed streets. Only the Via Sacra, a paved avenue leading from the Velia's heights to the Forum, was wide enough to take two wagons abreast. Elsewhere, houses were no more than ten feet apart; far less in many places. Sunlight was all but excluded, creating a gloomy warren of narrow lanes.

He ducked down low, using other pedestrians as cover. Romulus was expert at squeezing his boyish frame between people, worming past without anyone noticing. Within a few dozen paces, he would be totally indistinguishable from the crowd.

Gemellus' domus lay on the Aventine Hill, a mainly plebeian area just south of the centre. The trader had never seen fit to leave his roots behind, even when he could have moved close to the Forum Romanum itself. As in most parts of Rome, the dwellings of rich and poor were positioned side by side. Large houses with impassive stone walls and monumental gates sat beside insulae up to five storeys tall. These buildings contained the tenement flats in which most people lived.