The site remained unknown to the Western world until 1812, when it was introduced by Swiss explorer Johann Ludwig Burckhardt. It was described as "a rose-red city half as old as time" in a Newdigate Prize-winning sonnet by John William Burgon. UNESCO has described it as "one of the most precious cultural properties of man's cultural heritage." Petra was chosen by the BBC as one of "the 40 places you have to see before you die"
Pliny the Elder and other writers identify Petra as the capital of the Nabataeans and the centre of their caravan trade. Enclosed by towering rocks and watered by a perennial stream, Petra not only possessed the advantages of a fortress, but controlled the main commercial routes which passed through it to Gaza in the west, to Bosra and Damascus in the north, to Aqaba and Leuce Come on the Red Sea, and across the desert to the Persian Gulf.
Excavations have demonstrated that it was the ability of the Nabataeans to control the water supply that led to the rise of the desert city, creating an artificial oasis. The area is visited by flash floods and archaeological evidence demonstrates the Nabataeans controlled these floods by the use of dams, cisterns and water conduits. These innovations stored water for prolonged periods of drought, and enabled the city to prosper from its sale.
Although in ancient times Petra might have been approached from the south via Saudi Arabia on a track leading around Jabal Haroun ("Aaron's Mountain"), across the plain of Petra, or possibly from the high plateau to the north, most modern visitors approach the site from the east. The impressive eastern entrance leads steeply down through a dark, narrow gorge (in places only 3–4 m (9.8–13 ft) wide) called the Siq ("the shaft"), a natural geological feature formed from a deep split in the sandstone rocks and serving as a waterway flowing into Wadi Musa. At the end of the narrow gorge stands Petra's most elaborate ruin, Al Khazneh (popularly known as "the Treasury"), hewn into the sandstone cliff.A little further from the Treasury, at the foot of the mountain called en-Nejr, is a massive theatre, so placed as to bring the greatest number of tombs within view. At the point where the valley opens out into the plain, the site of the city is revealed with striking effect. The amphitheatre has been cut into the hillside and into several of the tombs during its construction. Rectangular gaps in the seating are still visible. Almost enclosing it on three sides are rose-coloured mountain walls, divided into groups by deep fissures, and lined with knobs cut from the rock in the form of towers.