All morning the men toiled at raising the breastwork over the remains of the gatehouse, and strengthening the inner wall. Mindful of Macro’s words, Cato drove them hard and permitted them few rest breaks as they thickened the makeshift defences and added to the height of the inner wall. If the enemy managed to force their way through this last obstacle then the Second Illyrian Cohort would be wiped out. As the men toiled within the fort, the enemy continued to clear away more of the traps laid outside, their workers screened by a thin line of archers ready to take a shot at any target that revealed itself up on the wall. Behind them the engineers sweated under the bright sun to make the surviving onager serviceable once again. Shortly after noon the enemy at last drew away from the siege engine as the throwing arm was carefully ratcheted back, engineers checking the weapon for any further sign of damage as it prepared to bombard the fort again. At length they were satisfied that it was safe to proceed. A curt order was shouted, the locking lever snapped back and the throwing arm swept up and hit the cross beam with a loud thwack as the missile was released, soaring up into the air and then arcing down towards the gatehouse. At once Cato and the work party dropped their tools and scrambled down behind the wall into cover.

The Parthian siege engineers were first rate, or at least very lucky, thought Cato, as the first shot smashed into the breastwork and knocked a gaping hole in the top of the rebuilt defences. The bombardment continued with an endless cycle of clanks, a crack and the crash and rumble of masonry. After the first missile had landed, Cato pulled his men back behind the inner wall and climbed a corner tower to watch proceedings as the hot afternoon wore on. The gradual destruction of the remains of the gatehouse was carried out in a methodical and complete manner, beginning with the wall and then simply pounding the rest into a pile of loose rubble that would make a practical breach for Bannus and his army to assault. As the light began to fade and the desert sand shimmered hot and bright red in the wash of the setting sun, the onager at last fell still and the men inside the fort no longer had to press themselves into the shelter of a wall and cringe as the rocks crashed down.When he was sure that the bombardment had ceased, Cato sent for Macro. The prefect joined him behind the destroyed gatehouse and took a few tentative steps on the rubble.

‘They’ll be able to climb over this easily enough.’

‘When do you think they’ll come?’ asked Cato.