History
Petra was first established sometime around the 6th century BC, by the Nabataean Arabs, a nomadic tribe who settled in the area and laid the foundations of a commercial empire that extended into Syria. Despite successive attempts by the Seleucid king Antigonus, the Roman emperor Pompey and Herod the Great to bring Petra under the control of their respective empires, Petra remained largely in Nabataean hands until around 100AD, when the Romans took over. It was still inhabited during the Byzantine period, when the former Roman empire moved its focus east to Constantinople, but declined in importance thereafter. The Crusaders constructed a fort there in the 12th century, but soon withdrew, leaving Petra to the local people until the early 19th century, when it was visited by the Swiss explorer Johann Ludwig Burckhardt.

Location
Petra lies about 3-5 hours south of modern Amman, about 2 hours north of Aqaba, on the edges of the mountainous desert of the Wadi Araba. The city is surrounded by towering hills of rust-coloured sandstone which gave the city some natural protection against invaders.
The site is semi-arid, the friable sandstone which allowed the Nabataeans to carve their temples and tombs into the rock crumbling easily to sand. The colour of the rock ranges from pale yellow or white through rich reds to the darker brown of more resistant rocks. The contorted strata of different-coloured rock form whorls and waves of colour in the rock face, which the Nabataeans exploited in their architecture.

The Siq
From the official entrance to the site, a dusty trail leads gently downwards along the Wadi Musa (The Valley of Moses). Situated in small rock outcrops to the left and right of the path are some small Nabataean tombs, carved into the dry rock. Beyond these, walls of sandstone rise steeply on the left, and a narrow cleft reveals the entrance to the Siq, the principal route into Petra itself.

The Nabataeans were expert hydraulic engineers. The walls of the Siq are lined with channels (originally fitted with chamfered clay pipes of efficient design) to carry drinking water to the city, while a dam to the right of the entrance diverted an adjoining stream through a tunnel to prevent it flooding the Siq.

Once inside, the Siq narrows to little more than five metres in width, while the walls tower up hundreds of metres on either side. The floor, originally paved, is now largely covered with soft sand, although evidence of Nabataean construction can still be seen in some places.

The Siq twists and turns, the high walls all but shutting out the early morning sunlight, until abruptly, through a cleft in the rock , the first glimpse of the city of Petra can be seen. Carved out of pale reddish sandstone, ornate pillars supporting a portico surmounted by a central urn and two flanking blocks, jut out from the cliff face ahead. This is The Khazneh