The Nabataeans built Petra over 1000 years ago. It was at the crossroads of Arabian trade routes (especially for spices and exotic oils like frankincense) linking China, India, Egypt and other Mediterranean cities. The Romans annexed it in 106 AD. But as trade routes shifted and demand for frankincense declined (as Christianity replaced other religions), Petra's inhabitants began to move away until the city was abandoned. It was used in the 14th century by the Crusaders but after that, it faded away until it was discovered in 1812 by a Swiss traveler.