They rode until dusk made further progress dangerous and then camped in the open, rising at the first hint of light to continue the chase. So it was that two days after leaving Heshaba they approached Petra in the blistering heat of noon.As they descended into the valley that led to the entrance of the city they passed a caravan heading north: hundreds of camels piled high with goods bound for the luxury-loving Hellenic cities of the Decapolis. Symeon, Murad and the others exchanged greetings with the men in charge of the caravan and stopped a moment for a brief conversation before they made their farewells and the caravan continued climbing the track at a slow steady pace.

Symeon reined his horse in alongside Macro and Cato. ‘I asked them if there had been any new arrivals in Petra earlier today, or yesterday.’

‘And?’ Macro responded.

‘It seemed that Bannus arrived at first light. They saw a party of horsemen enter the siq as the camels were being loaded. They had a boy with them, and a number of Parthians. It has to be Bannus.’

‘Siq?’ Cato asked. ‘What is the siq?’

Symeon smiled at him.’The siq is Petra’s secret weapon. You’ll see what I mean the moment we pass into it.’

They rode on, into the base of the valley, and became aware of a growing sound of voices, the braying of donkeys and the deeper grunt of camels, and then the track turned round a spur of rock and ahead of them lay a vast open area filled with men and beasts. Porters struggled with great bundles of goods: rolls of cloth, tightly bound packages of spices and fine glassware carefully packed in straw and placed in wicker baskets. Caravans were being loaded for the cities of the north, while others, unladen, were preparing to return to the great trading ports of Arabia for their next consignment of luxuries. Cato looked round eagerly. He had never seen the like of some of the people who thronged the great natural marshalling arena of Petra - brown-skinned, silk-robed men with narrow eyes, and dark hair in plaits. He pointed them out to Symeon and asked who they were.

‘They’re from the east.The furthest east a man can go, so I’m told. I don’t know much about them, except that they are as rich as men can be, thanks to Roman and Greek gold and silver. The amount of treasure passing through Petra is almost beyond imagination, Cato. I am surprised you Romans aren’t being bled white by such an outpouring of your wealth.’

‘You’ve never been to Rome, have you?’

‘Not yet. But I will, one day.’

‘Then you’ll see why Rome can afford these luxuries. There is nothing the richest men cannot buy. Their coffers are that deep.’

‘For the moment perhaps,’ Symeon mused. ‘But no empire, however rich, can continue indulging itself at such a rate, surely?