There are many ways to get into Petra, but none of them is easy, and if the valleys are blocked off, it is almost impossible for anyone to enter. The main entrance to Petra, called the Siq, is a very narrow gorge, with sides as high as 200 meters. A handful of people on them could hold off an entire army. This gorge and the temple, called the Kazneh, were used as a location in the American movie Indiana Jones and the Last Crusade and so became famous around the world. The remains of the ancient city of Petra have become a major tourist attraction in the Middle East. But what is the story behind this astonishing city? Who built it, and why?