Right on cue, the trumpets blew a short series of blasts. From the rear came the shouted order, 'Retreat to the ships!' The voice was calm and measured, quite at odds with the urgency of the situation.

'That's Caesar,' explained the legionary with a proud grin. 'Never panics.'

At once their lines began edging sideways, towards the western harbour. It was only a short distance, but they could not let down their guard at all. Seeing this attempt to escape, the Nubians yelled with anger and sprang forward again.

'Keep going,' cried the centurion nearest Romulus. 'Stop just before they hit. Stay in formation and drive them back. Then move on.'

Romulus eyed the triremes, which numbered about twenty. There would be room on board for all – but where would they go?

As ever, Tarquinius butted in with the answer. 'To the Pharos.' He pointed at the lighthouse. 'Over there, the Heptastadion is only fifty or sixty paces across.'

His confidence restored, Romulus grinned. 'We can defend that until doomsday.'

Yet the ships were still out of reach and, a heartbeat later, the Nubians struck the Roman formation with such force that the front ranks were driven back several steps. Screams filled the night air and soldiers cursed the bad luck sent them by the gods. Romulus saw a legionary to his left take a spear through one calf and go down thrashing. Horrendously, another had a blade pierce both cheeks to emerge on the other side of his face. Blood jetted from the wounds as the weapon was withdrawn. Dropping his scutum and sword, the soldier raised both hands to his ruined face and let out a thin, piercing cry. Romulus lost sight of both injured men as a mass of Nubians slammed up against his section.