'Those slingers can hit a bundle of straw at six hundred paces,' muttered Petronius.

More stones landed, closer this time. Romulus' gaze was drawn inexorably to the sharply outlined enemy figures, reloading their slings. Laughter carried through the air as leather straps swung hypnotically round their heads and then released – again.

Thankfully, the island was at last drawing near. Caesar had emerged on to the shore and was already screaming orders, guiding his men to defend their end of the Heptastadion. Romulus breathed a tiny sigh of relief. Safety was beckoning, and doubtless there would be some respite once they threw the Egyptians back. When that happened, he would force Tarquinius to tell him everything about the fight outside the brothel.

Still in the lead, the haruspex turned to say something. His eyes met with those of Romulus, which were flinty and full of resolve. Tarquinius' voice died in his throat and they simply stared at each other. The silent exchange spoke volumes, and set off a host of warring emotions in Romulus' heart. I owe him so much, he thought, yet he's the damn reason I had to flee Rome. But for him, I would have had a different life. Remembering the plain wooden sword owned by Cotta, his old trainer in the ludus, Romulus scowled. A rudis like that could have been mine by now.

Tarquinius stood up. He had reached the shallows.

Shouts rang out from the frustrated slingers. Reloading their weapons, they redoubled their efforts to bring down the trio. Hastily released stones pattered down harmlessly behind them.

Romulus pushed his caligae downwards, feeling mud squelch underfoot. Petronius let out a great sigh of relief. Two more strokes and he too was able to stand. The veteran released his grip and thumped Romulus across the shoulders. 'My thanks, lad. I owe you one.'

Romulus indicated the main force of Egyptians, which was massing for a full frontal attack along the Heptastadion. 'There'll be plenty of opportunity to repay me.'

'Get over here!' screamed a centurion, right on cue. 'Every sword matters.'

'Best do as he said,' advised Tarquinius.

They were the last words he spoke.

With a hypnotic whirring sound, a rock flashed through the air between Romulus and Petronius. It smashed into the left side of Tarquinius' face, audibly breaking his cheekbone. His mouth opened in a silent scream of agony and, spun to one side by the force of the impact, he dropped backwards into the waist-deep water. Half-conscious, he sank immediately.

Near Rome, winter 48 BC 'Fabiola!' Brutus' voice broke the silence. 'We'll be there soon.' Docilosa lifted the fabric side so that her mistress could look out of the litter. Dawn was fast approaching, but the party had already been on the road for more than two hours. Neither woman had complained at having to rise so early. They were both keen to reach Rome, their destination. So was Decimus Brutus, Fabiola's lover. He was on an urgent mission from his master Julius Caesar to confer with Marcus Antonius, the Master of the Horse. More troops were required in Egypt, to lift the blockade from which Fabiola and Brutus had only recently broken free. The enemy barricade still held Caesar and his few thousand soldiers captive within Alexandria.

Between the tall cypress trees which lined the road, Fabiola could make out plentiful brick-built tombs. Her pulse quickened at the sight. Only those who could afford it built such cenotaphs on the approaches to Rome. They were prominent sites which could not be missed by passers-by, thereby preserving the otherwise fragile memory of the dead. Brutus was correct: they were very close. The Via Appia, the road to the south, had the most mausoleums, mile after mile of them, but all routes into the capital were dotted with them. This, the road from Ostia, Rome's port, was no different. Decorated with painted statues of the gods and the ancestors of the deceased, the tombs were the dwelling places of cut-throats and cheap whores. Few dared to pass them at night. Even the dim pre-dawn light did not reduce the threat from the whispering trees and looming structures. Fabiola was glad of their heavy escort: a half-century of crack legionaries, and Sextus, her faithful bodyguard.

'You'll be able to have that bath at last,' said Brutus, riding closer.

'Thank the gods,' replied Fabiola. Her travelling clothes felt sticky against her skin.

'The messenger I sent ahead yesterday will ensure that everything is ready in the domus.'

'You're so thoughtful, my love.' She bestowed a beaming smile on Brutus.

Looking suitably pleased, he urged his horse into a trot and headed to the front of the column. Like Caesar, Brutus was not a man to lead from the rear.

Fabiola recoiled as the unmistakable reek of human waste carried to her nostrils. Thick and unpleasant, it was as familiar, but far less appealing, than that of freshly baked bread. It was Rome's predominant aroma, though, one which she had grown up smelling, and it had reappeared the instant their party had come within a mile of the walls. It was because countless thousands of plebeians in this teeming metropolis had no access to sewerage. The contrast with the cleanliness of Alexandria could not be more stark. She had not missed this aspect of life in the capital. While the light morning breeze made the odour less objectionable than during the sultry days of summer, it was already omnipresent.

At first Fabiola had been delighted about returning. Four years away from the city of her birth was a long time. The most recent of her temporary homes – Egypt – was an alien place, whose people hated their Roman would-be masters. Her resentment had vanished at the unexpected sight of Romulus on the battle-torn docks the very night she had left Alexandria. Naturally, Fabiola had wanted to stay and help him. Her twin was alive, and in the Roman army! To her immense consternation, Brutus had refused to delay their departure. The situation had been too desperate. In the face of Fabiola's distress, he was apologetic but resolute. She had had little choice but to defer to his judgement. The gods had seen fit to preserve Romulus' life this far, and with their help, she would meet him again one day. If only she'd understood his shouted words. His cry had been lost in the pandemonium of the trireme's departure; she could only assume he had been trying to tell her which unit he was serving in. Despite this, the encounter had given Fabiola a powerful new zest for life.

Now, after more than a week of hard travel, their journey was nearly over and, despite the thick fabric covering the litter, the air inside already smelt of shit.

Fabiola's stomach churned at the memory of the filth-encrusted bucket she and the other slaves had had to use in Gemellus' house. Never again, she thought proudly. How far I have come since that day. Even the brothel into which the merchant had sold her had possessed reasonably clean toilets. Yet this small improvement hardly counted against the degradation of strangers using her body for sex. The harsh reality of life in the Lupanar broke most women's spirit, but not Fabiola's. I survived because I had to, she reflected. Bent on revenge against Gemellus, and discovering the identity of her and Romulus' father, she had determined to escape her new career – somehow.

The list of rich men who frequented the whorehouse had been its most redeeming feature. Advised by a friendly whore to win over a suitable noble, Fabiola had cast her net far and wide, using her considerable charms to ensnare a number of unsuspecting candidates.

She lifted the heavy fabric and peered surreptitiously at Brutus, who was riding alongside the litter once more. Sextus too was within arm's reach; it was virtually his permanent position during daylight hours. At night, he slept right outside her door. Fabiola inclined her head, glad as always to have her bodyguard nearby. Then Brutus noticed her; a broad grin immediately split his face. Fabiola blew him a kiss. A career soldier and loyal follower of Caesar, Brutus was courageous and likeable. After a number of visits to the Lupanar, he had fallen utterly into her thrall. Not that she had decided on him for that reason, of course.