At the end of the Siq—a narrow, winding gorge through ruby-red sandstone in southwestern Jordan—lies one of the most jaw-dropping sights in archaeology: an open plaza dominated by Al-Khazneh, an elaborate, colonnaded tomb cut directly out of the vermilion cliffs. Welcome: You’ve made it to Petra, the “Rose City,” one of the New Seven Wonders of the World.Archaeological evidence indicates that humans settled the land that became this ancient hidden city as early the Paleolithic era. This part of Jordan is also religiously significant: Petra is part of Wadi Mūsā (the Valley of Moses), where it is believed Moses performed a miracle to quench the thirst of the Israelites against God’s wishes. The site as we know it today, however, was established centuries later by the Nabataeans, an Arabic tribe who made Petra their kingdom’s capital from the second century B.C.E. to 106 C.E., when the kingdom was absorbed by the Roman Empire.Halfway between the Dead Sea and Red Sea, Petra sat at the crossroads of several crucial trade routes connecting the Arabian Peninsula to Greece, Egypt, and China. Petra’s location linking East and West—which swiftly enriched the city and, by extension, the entire Nabataean Kingdom—is reflected in its distinctive rock-cut architecture, which infuses Nabataean architecture with Hellenistic and Byzantine features. Many of Petra’s surviving rock-cut buildings, for instance, have columns despite the fact that they are structurally superfluous.Who were the Nabataeans?Though the Nabataeans settled permanently in Petra, for much of their history they were a nomadic Bedouin people who traveled the Arabian Desert. Why, exactly, they chose to settle permanently in Petra is unclear. On its own, Petra’s desert climate would be uninhabitable, but the Nabataeans’ sophisticated irrigation system supported the agriculture necessary to feed its inhabitants (10,000 to 30,000 at its peak).The kingdom appears to have been annexed peacefully by the Romans in 106 C.E. In the fourth century, when the Roman Empire became Christianized as the Byzantine Empire, churches were built in Petra, some of them supplanting once-sacred tombs. A view of Petra, Jordan photographed between 1898 and 1946.When was Petra abandoned?During the Roman occupation, changes in trade routes redirected wealth away from the city, leading to a decline in status and population. Its death knell came in 363 C.E., when a catastrophic earthquake destroyed much of the city. Scholars believe Petra was more or less uninhabited by the seventh or eighth century—at least by permanent residents. Nomadic Bedouin tribes have long sought temporary refuge in the city. In fact, when Swiss explorer Johann Ludwig Burckhardt encountered Petra in 1812, reintroducing the site to the West, he was led there by a Bedouin guide. Bedouins still lived there until 1985, when they were forced out by the Jordanian government once Petra was named a UNESCO World Heritage Site.What buildings survive at the site today?Petra’s most striking structures remain its rock-cut monuments. Most, like Al-Khazneh, are tombs; the largest and grandest is the Monastery, one of the buildings likely repurposed as a church during the Byzantine era. Petra’s Theatre, which likely could hold some 8,500 spectators, is also cut into the rock face but was heavily damaged during the 363 earthquake.In addition to its rock-cut architecture, several freestanding structures survive. A pool and garden complex is still remarkably intact, as are the remains of a column-lined street.In 2016, satellite imaging and drone surveys revealed a massive structure—about the size of two Olympic swimming pools placed side by side—submerged in sand half a mile south of Petra’s city center. The structure has not been excavated, but the imaging indicates that it is a large, raised platform with a smaller building on top of it. If researchers’ hunches are right, it is the second-largest extant structure in Petra after the Monastery, and possibly the oldest.