Petra, Arabic Baṭrā, ancient city, centre of an Arab kingdom in Hellenistic and Roman times, the ruins of which are in southwest Jordan. The city was built on a terrace, pierced from east to west by the Wadi Mūsā (the Valley of Moses)—one of the places where, according to tradition, the Israelite leader Moses struck a rock and water gushed forth. The valley is enclosed by sandstone cliffs veined with shades of red and purple varying to pale yellow, and for this reason Petra was called by the 19th-century English biblical scholar John William Burgon a “rose-red city half as old as Time.” The modern town of Wadi Mūsā, situated adjacent to the ancient city, chiefly serves the steady stream of tourists who continue to visit the site.

The Greek name Petra (“Rock”) probably replaced the biblical name Sela. Remains from the Paleolithic and Neolithic periods have been discovered at Petra, and Edomites are known to have occupied the area about 1200 BCE. Centuries later the Nabataeans, an Arab tribe, occupied it and made it the capital of their kingdom. In 312 BCE the region was attacked by Seleucid forces, who failed to seize the city. Under Nabataean rule, Petra prospered as a centre of the spice trade that involved such disparate realms as China, Egypt, Greece, and India, and the city’s population swelled to between 10,000 and 30,000.

One tradition has the Three Wise Men buying their gold, myrrh and frankincense at Petra on their way to Bethlehem. The greatest Nabataean king was Aretas IV (9 BC to AD 40), whose rule extended as far north as Damascus. His daughter Phasaelis was married to Herod Antipas, who divorced her to marry Herodias, his brother’s wife. Aretas IV then marched on Herod’s army, defeated it and captured territories along the West Bank of the Jordan River.

When the Nabataeans were defeated by the Romans in 106 CE, Petra became part of the Roman province of Arabia but continued to flourish until changing trade routes caused its gradual commercial decline. After an earthquake (not the first) damaged the city in 551, significant habitation seems to have ceased. The Islamic invasion occurred in the 7th century, and a Crusader outpost is evidence of activity there in the 12th century. After the Crusades the city was unknown to the Western world until it was rediscovered by the Swiss traveler Johann Ludwig Burckhardt in 1812.

Also, here on Mount Hor, or in Arabic, "Jabal Harun" (Aaron's Tomb) we can find the Tomb of Aaron, the brother of Moses.