The Great Earthquake
Petra has suffered many earthquakes during its long history. The city sits near the boundary of the Arabian plate, one of about a dozen large, moving landmasses that make up Earth's outer shell. Regions where plates intersect are prone to earthquakes; in the eastern Mediterranean three plates come together, so Petra and its surrounding area are at particular risk.
A quake on May 19, AD 363 seems to have struck Petra an especially heavy blow. Contemporary records claim half the city was destroyed, and archaeologists confirm considerable damage to Petra's main theater, its major temples (including the Qasr al-Bint), and the Colonnaded Street. Even worse, the quake disrupted the water supply system. An economically healthy Petra might have rebounded, but changes in trade routes had already sapped the city's vitality. By AD 363, it seems, Petra had lost the means to rebuild itself.
How Do We Know?--The Quake Date
In 1976, archaeologists in Petra excavated a small house destroyed by an earthquake in antiquity. Lying in one corner were what seemed to be the remains of a spare-change jar: 85 small bronze coins scattered amid pottery fragments. All the coins bore the image of the Roman emperor Constantius II, and most were minted after a currency reform of AD 354. The quake, therefore, could not have happened before then.
Additional evidence came to light that same year when a scholar doing archival research chanced on a letter written in antiquity. Evidently the work of Cyril, bishop of Jerusalem from AD 350 to 386, the letter tallies the effects of a great regional earthquake. According to the letter, "nearly half" of Reqem (the Nabataean name for Petra) was destroyed by a quake "at the third hour, and partly at the ninth hour of the night," on May 19, AD 363. Cyril tells us, in other words, the date and time not just of the main quake, but of its powerful aftershock.