He stepped back and nodded to the sentry. As quietly as he could, the sentry slid back the bolts of the sally port and eased the door open.There was a faint grating squeal from the hinges and Macro sucked in his breath at the sound that seemed so loud in the stillness behind the wall. The sentry paused for a moment and then opened the door more slowly, until there was a sufficient gap for Cato and his men to file through.

‘Come on,’ Cato whispered, and with a last reassuring glance towards the dark shape of Macro he crept out of the fort. The sky was moonless and dim grey strands of cloud covered most of the stars so the landscape was wrapped in darkness - perfect cover for Cato and his party. Of course, the same lack of illumination was the main danger facing the Romans. It would be easy enough to stumble into an enemy sentry or a patrol in such conditions. That was why Cato was determined to proceed as cautiously as possible. As the last man exited the fort the sally port was gently closed behind them. Cato waited a moment for any sign or sound that their presence had been detected, and then he beckoned to the man behind him and began to creep along the foot of the wall. In the distance they could hear the sounds of the men at the main gate, hurriedly trying to repair some of the damage done to the gatehouse during the day. The night’s labour would be undone in the first few hours if the bombardment continued in the morning, but it would gain the garrison a little more time. Cato headed towards the narrow path that led from the north face of the fort.

As they reached the point where the lamp glowed faintly on the wall Cato halted, and let his men catch up. Already he was shivering, partly from the penetrating cold of the air and partly from the state of nervous excitation as he led his men on this dangerous raid into the enemy camp. He took a deep breath to try to calm his anxiety, and then headed down into the ditch that surrounded the fort, and climbed up the far side. Picking the black mass of a distant rocky outcrop as a landmark he began to feel his way towards it on hands and knees. His left hand recoiled from contact with the sharp point of a caltrop and he felt ahead and soon found another to give him some sense of that side of the passage.They had crept over a hundred paces from the wall, by Cato’s reckoning, before he glanced back and saw the lamp at headquarters as well, almost perfectly aligned with the other one on the wall. He adjusted his position until the two lamps were in line, and then continued forward slowly.