Cato tore his sword from the scabbard and slung the latter aside as he ran hard towards the fight. Bursting out from between the last pair of barracks he glimpsed two or three men holding horses to one side and a score of others, Thracians, around the inner gate engaged with a handful of men defending the passage. Then he saw that the smaller group were carrying legionary shields and wearing Roman helmets. One even had the crest of a centurion. So that was it. Caratacus had used some captured kit to trick his way into the fort.

Macro called out again. ‘Don’t let ’em get out, lads!’

Out? Cato abruptly scrambled to a halt. What was this? What was happening? More men were emerging all around the gatehouse, some bearing torches they had hastily snatched up from the watch fires that burned through the night. By their light the scene became clear. Quertus and a band of his men were trying to cut their way through the section of legionaries manning the gatehouse, and the duty officer, Macro. As more men arrived on the scene, they hesitated as they saw the skirmish, not sure what to do, which side to take in the unequal fight. The Thracian commander looked up, his expression wild and fearful.

‘Kill them!’ he shouted to his followers. ‘Now, or we’re dead men!’

Cato strode forward, sword held ready. ‘Quertus!’ he bellowed. ‘Throw down your weapons, you and your men. Do it now!’

The Thracians at the gate backed away from the legionaries uncertainly, turning towards the approaching prefect. Around them, in a growing ring, stood the legionaries and auxiliaries roused from their sleep by the alarm. Cato grasped what must have happened and he stopped a safe distance from Quertus.

‘You’re trying to desert . . . Centurion Petillius!’

‘Sir?’ the officer responded from the gathering crowd.

‘Get your men over to the gate at once!’

‘Yes, sir! Legionaries! On me!’

Men surged forward and took position between the Thracians and the gate. There was enough light now for Cato to see the horse holders clearly and he gave a start.

‘Decimus? What in the name of the gods are you doing?’

His servant shrank before his superior’s gaze, and then released the reins of the horses he was tending and edged forward, glancing from Cato to Quertus and back again. Then he hurried across to join the ranks on either side of the Thracian officer. The other handlers followed his cue and ran across to join their leader. In amongst them he saw Maridius, arms bound to his side. Cato glared at them all, still unwilling to believe the evidence of the treachery before his eyes. Then he turned to the gate. ‘Macro!’

There was no reply. Cato edged round and joined Petillius and his men. ‘Macro! Speak up, man!’