As the Thracian straightened up, movement out in the valley caught his eye, and at last he saw the horsemen, no more than half a mile away, coming on at a brisk trot. There were little dots in his eyes as he stared at the rapidly approaching figures – at least ten and not more than twenty. The rising sun glinted red off helmets and spear points, which meant that they were well armed, but they did not ride in a neat column – more like a swarm – and that surely meant that they were Britons.

The Thracian had not seen an enemy since he had come here, back in the winter. He strained to see more clearly, in case this was about to change, while praying that it was not. The Britons swept past the herd boys and their cows, ignoring them, and the children did not seem to be afraid of them, which was a good sign.

The leading rider was a tall man on a big horse and even though he could not make out his face, the Thracian recognised him and breathed a sigh of relief. It was Vindex, leader of the scouts who served with the army. He and his men were frequent visitors, and the centurion often rode out with them, but they had not been here for nearly a month.

‘Tower, there!’ Crescens yelled up from the courtyard, interrupting his thoughts. ‘Anything to report?’

‘Omnes ad stercus,’ the Thracians said wearily. There was no more time. Taking just a moment to aim, the Thracian lobbed the apple core, and felt considerable satisfaction when it struck the shallow neck guard of the boy’s iron helmet. The young sentry jerked awake with a grunt, still groggy as he turned and looked up, his face very pale.

‘Do your job, boy,’ the Thracian shouted, pointing at the horsemen. It no longer mattered if he made any noise. He looked back over his shoulder. ‘Riders coming in!’

Below him the lad was still sluggish as he looked in that direction. He stared for a moment, and then gasped, dropping his spear. The Thracian laughed as the boy, gaping, raised his own arm to point, the movement making his shield fall flat on the grass.

‘Yes, I know,’ the old soldier said under his breath, ‘I see ’em. And how’s your laundry doing, sonny-boy?’

The horsemen were close enough to count fourteen riders and three more horses carrying burdens. The sun had cleared the hill and cast long shadows behind them as they pounded up the path towards the gate. The Thracian stepped over to the bell and rang it six times to announce the rising of the sun. He waited for three breaths before ringing it again to sound the alarm, not that he thought there was anything to worry about, but because that was the rule.

‘Scouts coming in,’ he shouted down into the courtyard. ‘Open the gate!’