Nabataean architecture

The Nabataeans are traders. Frankincense, myrrh and spices pass through their land on the way to the Mediterranean, and they make a fortune taking tolls.

In the 4th century BC they settle in a valley in today's Jordan. Two hundred years later Petra is the capital of a kingdom. You reach the city through the Siq, a narrow gorge between rock walls – and at its end Al-Khazneh, "the Treasury", opens up.

It is no treasury. It is probably a tomb, perhaps King Aretas IV's, carved in the 1st century AD. Columns, pediments and a round pavilion in the middle – a Greek palace façade, cut straight out of the sandstone. Behind it lie only a couple of bare rooms.

That is the Nabataean trick. The trade routes brought them into contact with the Hellenistic world, and they borrow its forms. But they don't build. They carve.

Further south, in today's Saudi Arabia, lies Hegra – the kingdom's second city under Aretas IV. Here more than a hundred tombs are carved into free-standing outcrops in the desert, and the largest, Qasr al-Farid, is called "the lonely castle".

In AD 106 Rome takes over the kingdom. Petra is forgotten by the West until the Swiss traveller Johann Ludwig Burckhardt reaches it in 1812.

Ancient Greek architecture. The columns and pediments are Greek in form. But a Greek temple is built of blocks; a Nabataean façade is carved from the mountain, and there is seldom much behind it.

Roman architecture. Rome takes over Petra in AD 106 and builds a colonnaded street and a theatre there. The Roman stands free – the Nabataean sits in the rock.