Those men who had already notched their first arrow braced their legs apart, leaned back and drew their bows, adjusting the angle to get the maximum range.Then they waited a moment, until the Roman patrol was close enough to the fort to ensure that the arrows would pass over them. The first man released his bowstring and the shaft shot high into the air, arcing up into the clear blue sky before it seemed to hang a moment and began to fall to earth. From where Cato stood it seemed that it would surely fall amongst the men of the patrol pounding towards the fort. He gritted his teeth as the arrow plummeted down. Only at the last moment was it clear that it had overshot the patrol, and it struck the ground just ahead of their pursuers with a small explosion of sand and dust.

‘The range is good!’ Macro shouted. ‘Let ‘em have it!’

More shafts flitted up into the sky and when they fell they were right on target. Cato saw one of the pursuers struck in the face and the man threw his hands up and tumbled off the back of his horse, disappearing under the hooves of the beasts galloping behind. A thin cry cut through the air and the Parthians instantly dispersed, swerving out to both sides to present a more difficult target to the Roman archers. But they had lost their prey. The gate was open and the surviving men from the patrol charged towards it, careering through the arch into the safety of the fort beyond.

‘Close the gate!’ Macro bellowed an instant later and the hinges grated and then the gate slammed into place with a thud that could be clearly felt in the tower above. At once the Parthians wheeled their mounts round, and then tore off back into the desert and out of range of the archers on the walls. Cato watched them go for a moment and then turned to the other officers.

‘I think the situation’s just become a lot more serious.’

‘Parthians,’ Longinus muttered. ‘Bloody Parthians. Always the bloody Parthians.’

Macro gestured to Cato. ‘Come on. We have to speak to the men from that patrol.’

They climbed down from the tower and joined the cluster of men surrounding the survivors of the patrol and their mounts. The horses’ coats were stained with sweat and streaks of foam and their flanks heaved as they snorted. Macro thrust one of the men aside.

‘Make way! Make way there!’