The other man looked at him closely. ‘How long are you expecting to stay here then?’

Macro cursed himself for the slip. He forced himself to grin. ‘As little time as possible. Knowing the army, that probably means I’ll end up dying of old age at Bushir. Long after the army bureau has forgotten that they sent me here in the first place. If I’m really lucky they might remember me, and even cough up a small pension.’

‘Small is the word,’ Postumus said with feeling, and then stared into the distance as he continued, ‘That’s why a man should build up a little contingency fund, if circumstances permit.’

Macro looked at him. ‘What do you mean?’

Postumus’ lips flickered into a quick smile. ‘You’ll see. All in good time. No . . . Wait.’ He suddenly thrust his arm out and pointed towards the horizon. ‘There! Look.’

Macro followed the direction of his finger and squinted at the shimmering haze. ‘What? I don’t see anything.’

‘Look again. Closely.’

At first Macro could see nothing, but when he strained his eyes a small black dot blinked into sight, and then another to one side. In the next few moments several more appeared and the first slowly resolved itself into the distant silhouette of a man riding a strange-looking mount. It took a while before Macro realised that it must be a camel.

‘Who are they?’

‘Traders,’ Postumus replied. ‘They come from Aelana. It’s an Arab colony on the coast. They land goods from the far east and load them into caravans bound for Palestine, Syria, Cilicia and Cappadocia. It’s quite a haul from Aelana, and parts of the route pass through some pretty wild territory. That’s where the Nabataeans come in, and more recently us.’

Macro frowned. ‘I don’t get it.’

‘How do you think the Nabataeans became so wealthy?’

Macro shrugged.

‘It’s a protection racket. Their kingdom sits astride some of the most profitable trade routes in the known world. So they sit pretty in Petra and demand a toll on any caravans passing through their lands.At the same time they offer their services to protect the caravans from those tribes deep in the desert that occasionally raid the trade routes.’

‘I see,’ Macro replied. ‘So what’s our part in this?’

‘It’s our duty to police the trade route passing to the east of the fort.That’s where Roman territory begins and Nabataea ends.That’s why we’re here, to protect caravans, like that one. It’s a mutually beneficial arrangement.’

‘I see.’ Macro stared at him. ‘You mean, you protect them at a price?’

‘Of course.’ Postumus laughed. ‘All part of the service that the Second Illyrian provides to its regular customers.’

‘I see,’ Macro said again. He stared at the caravan, his mind racing. It was as he suspected. The question was what should he do about it, if anything. ‘How does it work?’