A few shots later, the corner of the gatehouse collapsed on to the ground outside the fort and once the sound of crumbling masonry had died away the defenders could hear the triumphant cries of the enemy. Cato glanced up at the gatehouse and saw the wide gap in the top of the wall next to the collapsed section, as if some great Titan had torn a chunk of the defences away with his teeth. And still the bombardment continued without let-up. Indeed, once the corner had given way, Cato steadily counted between impacts, and calculated that the enemy had increased the frequency of the rocks they were lobbing at the fort. Each blow on the loosened stonework caused more of the structure to collapse on to the existing rubble with a rumble of heavy masonry and the slither and rattle of smaller stones.As the sun sank towards the horizon behind the enemy camp the ruin of the gatehouse became a jagged silhouette, until at last the arch above the gate fell in and all that remained was a tangled heap of rubble and shattered beams of wood.

As dusk fell across the surrounding desert Macro and Cato climbed into one of the corner towers to survey the situation. Some of the enemy, emboldened by the destruction of the gatehouse, had ventured close enough to the fort to attract the attention of the archers stationed at intervals along the wall and every so often an arrow whirred out from the fort towards the nearest men, causing them to scatter and dive for cover. Macro was cheered by the sight of one man, slower to react than his companions, who happened to look up just as the heavy barbed tip of a shaft smashed into his face and burst out the back of his skull.

'Fine shot!' Macro bellowed along the wall and one of the archers quickly turned to bow his head in acknowledgement before quickly notching another arrow and looking for his next target.

As the last of the light began to fade the enemy pounded what was left of the gatehouse and then ceased the bombardment. They would resume in the morning and after a few more hours the breach would be practicable for Bannus and his army to assault. Fires appeared in the enemy encampment and the sounds of singing and laughter could be clearly heard by the defenders as they continued to build up the inner wall. Macro and Cato inspected the work of their men by torchlight. The new wall rose to a height of nearly eight feet and was thick enough to withstand the pressure of a wave of men pressing up against it. On the inside stood a narrow fighting platform from which the defenders could strike down on the enemy as they clambered over the rubble strewn across the ground in front of the wall.

Macro patted the rough surface. 'It'll do.'

'It will have to,' Cato replied softly. 'When they finish off what's left of the gatehouse, that's all there is to keep them out.'

By the wavering glow of the torch he held in his hand Macro turned to stare at his friend. 'You're right, of course. They will finish the job in the morning.'

'Unless something is done about those onagers tonight.'

'I told you,' Macro responded wearily. 'It's too dangerous.'

'We're in danger either way,' said Cato. 'At least if we try something we might be able to set them back a day or so and buy ourselves some time. It has to be worth trying, sir.'

Macro wasn't convinced. 'I told you, whoever goes out there under cover of darkness is bound to lose their way through the defences.'

Cato was looking at Macro's torch and Macro noticed the excited glint in his friend's eyes that always accompanied the sudden rush of thought when Cato came up with one of his hare-brained schemes. He felt his heart sink.

'Let me lead a raid, sir.'

'Are you so tired of living already, Cato?'

'No, I'm just not terribly keen on sitting here, waiting to be killed. Besides, I think there's a way of safely passing through our defence lines…'

'Are you sure about this?' Macro said softly as he looked at Cato.The young centurion had blackened his face and the rest of the flesh that was not covered by the dark brown tunic that he wore. His sword belt was buckled round his waist and a haversack hung from his shoulder containing a tinderbox and several small pots of oil. Behind him stood a party of twenty men, similarly equipped for the night's work.

'I'll be fine, sir. Just make sure those lamps are kept alight.' Cato nodded up to the rampart where the wan glow of an oil lamp flickered in the darkness. Back at headquarters a second lamp had been lit and placed in the highest window in line with the lamp on the wall and the narrow path through the screen of traps and obstacles that stretched out beyond the north wall of the fort.

Macro clasped his friend's arm. 'Do what you have to do and come straight back. Don't get carried away. I know what you're like.'

Cato grinned. 'Trust me, sir. I don't want to be out there any longer than I have to.'

Macro gave Cato's arm a brief squeeze. 'Good luck then.'

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.

It took a long time to reach the limit of the defences that Macro had prepared and Cato felt a hand on his shoulder as the man behind grasped him suddenly. Cato turned and saw his arm pointing away to the right. Less than a hundred yards away Cato could just make out the silhouettes of two Judaeans against the marginally lighter night sky.There was a snatch of conversation and laughter and the two figures moved slowly away, continuing their patrol around the fort's perimeter. The small party of Romans continued forward until they were well clear of the defences and then Cato turned parallel to the fort's wall and led them towards the red gloom of the fires in the enemy camp.