Oddly, his most pressing concern was not the mission itself, or even his own slim hope of survival, but the attitude of the men. Aulus, the ringleader of the attempted mutiny, remained scowling and aloof. Narses and Zabda, the two easterners from the waterfront bar in Zuegma, often came close to dumb insubordination. On the march, they muttered together as they shepherded the baggage animals; the bushy beard of the Persian and the wispy one of the Palmyrene both nodding. Decimus, the handsome master of horse, and Clemens, the old armourer, were punctilious in obeying orders, replied when spoken to, but seldom volunteered anything. At least Quintus, as if to atone for his role the morning after the death of Severus, was happy to talk, and Hairan, the third easterner, was affable to Valens as to everyone. And then there was always Iudex. His appearance might be slightly disconcerting, and his conversation sometimes unfathomable, but he liked to talk. Yet for Valens it was unthinkable that an equestrian officer should unburden himself to common soldiers under his command, even to those who appeared sympathetic.

They had eaten. Quintus was studying the moonless sky. Iudex was carefully washing his big hands. Clemens and Aulus were out on guard. The rest were already asleep.

Valens watched Iudex. His ritual ablutions complete, the bald man stood facing north. ‘Restrain my heart and mind from the turmoil of sin, and let me ascend on the road of peace.’ Iudex said the words reverently. With an agility surprising in such a large man, he got down on bended knee, then prostrated himself full length on the ground. ‘May I become perfect in mind, spirit and body, and through your power, Lord, may I conquer the deceitful demons of my soul.’

Iudex prayed seven times a day. On the march, he would pull his horse out of the line and dismount. Frequently he was left behind, out of sight. Soon after, his sky-blue cloak would appear as he cantered after the column. Resuming his station, his cherubic features were suffused with happiness.

The piety of this strange soldier unsettled Valens. No matter how bizarre the cult to which he belonged, Iudex had a god in which to believe, a beneficent power to look to for succour and guidance. Valens missed the faith of his childhood. He had never felt so alone as he did now. To avoid the temptation of opening a flask of wine, he walked over to talk to Quintus.

‘How do you plot a course by the stars?’

‘There is no great mystery.’ The navigator had large, thoughtful eyes in a delicate face set under wavy, swept-back hair. It gave him a look of youthful and sensitive intelligence.

‘I would like to know.’

‘We do not follow the stars which wander across the heavens. Instead, the never-setting pole star, the brightest in both the Bears, is the certainty that underpins all calculations.’

Valens looked where Quintus pointed.