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?'

Postumus had been watching him closely, and appeared relieved that Macro did not seem to be one of the sticklers for the strict letter of the law. 'It's simple enough. We have a regular deal with most of the caravan cartels. Just as the Nabataeans do.They get an escort from Aelana to Petra and from there to Machaeros, where there's another way station like this. That's the limit of Nabataean authority. They used to escort them as far as Damascus, but we handle the last stage of the job these days.They tried to undercut us, but we made it clear that this is now our turf and the Nabataeans keep clear of us. We pocket the fee and see them safely as far as the Decapolis.'

'Not exactly by the book, is it?'

'No. But not exactly illegal, either.' Postumus replied. 'We carry out our duties patrolling the frontier, and the caravan cartels get their escort. Everyone's happy. The thing is to make sure that word of this doesn't spread too far, or pretty soon we'll have Cassius Longinus clamouring for a cut, and the procurator in Caesarea. So we keep it quiet.'

'I can imagine.'

'Of course, the only really tricky issue is when we have to deal with fresh customers. Those caravan cartels that are new to the area. Like that one.'

'Oh? What happens then?'

'You'll see.' Postumus turned towards him. 'When they reach us, let me do the talking, sir. Chances are they'll know some Greek but they prefer to negotiate in their lingo and I know enough to get by.'

'All right then.' Macro nodded. 'I'll follow your lead.'

The caravan emerged from the heat haze and slowly drew closer to the way station. Macro watched them from the tower, and saw that there must be at least a hundred camels, weighed down by great baskets stuffed with bales of material, jars tightly packed into straw and other less discernible goods. Towards the front of the caravan were two large ox-carts laden with stout lengths of timber.The camels came at a steady swaying pace, goaded on by the herders walking at their side, who occasionally flicked the beasts with the ends of the slender canes they carried. On either flank of the caravan rode a handful of guards: warriors swathed in dark robes, with swords and bows slung from the wooden frames of their camel saddles. They looked fierce enough, Macro decided, but there were only twelve of them, hardly sufficient to beat off a spirited attack.

Down below in the courtyard of the station Postumus was ordering his men to mount up, and with a last look at the approaching caravan Macro descended from the tower to join them. As soon as he was in the saddle Postumus gave the signal to move and the horses clopped out of the way station and into the harsh light outside. They quickly fanned out and formed a line two deep across the track, the standards of both squadrons prominently on display a short distance in front of the main body.

'Just to make sure they know we're Roman,' Postumus explained to Macro. 'No sense in panicking them.'

Even so, the caravan halted. The escorts formed a small party with the merchants in charge of the caravan and warily approached the Romans. They stopped the moment they were within speaking distance and one of the merchants waved a hand in greeting.

'Remember, sir,' Postumus muttered, 'let me do the talking.'

'Be my guest.'

Postumus clicked his tongue and walked his horse forward. Macro followed him, keeping a short distance behind. They reined in a few paces from the other men.

Postumus flashed a smile and addressed them in Greek. 'I bid you welcome to the Roman province of Judaea. Do any of you speak Greek?'

'I speak it, a little.' One of the men lowered the veil covering his mouth so that Postumus would know who was speaking for the caravan. 'What can I do for you, Roman?'

'It's more a question of what I can do for you.' Postumus bowed his head.'The route ahead is plagued by raiders from the desert. You will need a stronger escort than that afforded by your twelve companions, no matter how formidable they might be. My men and I can ensure your safe passage through this area as far as Gerasa, should you wish it.'

'Most kind of you, Roman. I imagine you will require us to pay a fee for this service?'

Postumus shrugged.'A small consideration is all that is required.'

'How much?'

'A thousand drachma.'

There was a stony silence from the leader of the caravan, until one of his fellow merchants broke the silence and spoke harshly in their tongue. A conversation ensued and Macro caught the angry tone in their voices. At length the leader hushed his friends and addressed the centurion again. 'It is too much.'

'It is what all caravans who pass this way pay us, should they require our protection.'

'And if we don't pay?'

'You may freely pass. But you continue your journey at your own risk. It is not advisable.You are new to this route, are you not?'

'Perhaps.'

'Then you might not be fully aware of the dangers.'

'We can look after ourselves.'

'As you wish.' Postumus twisted round in his saddle and bellowed an order for his men to move off the track. Then he turned back to the leader of the caravan, bowed his head politely and turned his horse about to trot off and join his men. Macro caught up with him and edged his beast alongside.