His gaze shifted to the last five sections of the German auxiliaries marching behind the wagons. While they might not look like proper soldiers, Balbus knew that they were good in a fight, and their reputation was such that only the most foolhardy of brigands would dare to attack the convoy. Anyway, the danger, such as it was, had passed as the convoy descended on to the broad flat valley of the River Po.

He clicked his tongue and pressed his boots into the flanks of his mount. With a brief snort the horse lurched forward into a walk and Balbus steered it back on to the road, passing the leading ranks of auxiliaries and their commander, Centurion Arminius, until he had resumed his position at the head of the convoy. They had made good time. It was not yet noon and they would reach Picenum within the hour, there to await the Praetorian escort if it had not already reached the town.

They were still some two miles from Picenum when Balbus heard the sound of approaching horses. The convoy was passing through a small forest of pine trees whose sharp scent filled the cold air. An outcrop of rock a short distance ahead obscured the road beyond. Balbus instinctively recalled his days on the Danube where the enemy’s favourite trick was to trap Roman columns in similar confined settings. He reined in and threw his hand up.

‘Halt! Down packs!’

As the wagons rumbled to a standstill, the German auxiliaries hurriedly set down their marching yokes, laden with kit, on to the side of the road and closed ranks at the head and tail of the convoy. Balbus passed the reins into his left hand, ready to draw his sword, and glanced round into the shadows beneath the trees on either side. Nothing moved. The sound of hoofbeats grew louder, echoing off the hard surface of the paved road and the rocks. Then the first of the riders came into view round the bend, wearing the red cloak of an officer. His crested helmet hung from one of the saddle horns. Behind him rode another twenty men in the mud-spattered white cloaks of Praetorian Guard rankers.

Balbus puffed his cheeks and let out a sharp sigh of relief. ‘At ease!’

The auxiliaries lowered their shields and the shafts of their spears, and Balbus waited for the riders to approach. Their leader slowed his horse to a trot and then to a walk for the last fifty paces.

‘Tribune Balbus, sir?’

Balbus looked closely at the other officer. The face was familiar.

‘What is the correct challenge, Centurion?’ he demanded.

‘The grapes of Campania are ripe to pick, sir,’ the other man replied formally.

Balbus nodded at the phrase he was expecting to hear. ‘Very well. You were supposed to wait for us at Picenum, Centurion . . .’

‘Gaius Sinius, sir. Centurion of the Second Century, Eighth Cohort.’