In the 11th centruy, Petra lay abandoned. The silence of was broken by the arrival of the Crusaders in the early 12th century. Some Christian monks, who still inhabited the Monastery of St. Aaron on Jebal Haroun, the highest mountain in Petra area, asked King Baldwin I of Jerusalem for help as they were under threat from Saracen raiders on the ancient trade route. Baldwin then realized the strategic importance of this area, and established the district of Oultre Jourdain, an outpost of the Kingdom of Jerusalem. The people of the area resisted the crusaders and were punished by being smoked out of the caves in which they lived.

To defend their new territory, the Crusaders built a string of fortresses in the eastern mountains. In the area they called Li Vaux Moise, or the Valley of Moses (Wadi Mousa) the largest and strongest castle was built just outside Petra. A smaller fort was built on al-Habis, a high point in the heart of the ancient city to complete their signaling sight-line to Jerusalem. The fortifications of Outre Jourdain were strengthened after several major clashes with Muslim forces culminating in the construction of the great Crusader fortress at Kerak (Le Krac des Moan) in 1142.

The Li Vaux Moise castle was abandoned in 1189, the last of the eastern fortresses to surrender to Salah ad-Din (Saladin). The Christian Pilgrim, Theitmar, refers to Petra's fortresses in 1217 and several later Arab writers mention the former Crusader fortresses at Petra. The Arab geographer, Yaqut al-Hamawi, in 1225, lists castles named Al Wu'eira and Selah near Wadi Mousa. The Mamluke Sultan, Baibars passed through Petra in 1276 on his way to suppress a political revolt at Kerak. His chronicler, Muhdi el-Din Ibn 'Abd el-Zaher, mentions the fortress of Al Aswit (probably Al Habis castle) at Petra.

During the following centuries sandstorms and floods eroded the monuments, and sand and debris flooded down the ravines burying much of the city under tons of debris. As far as the west was concerned, all knowledge of Petra and the Nabataeans was lost. Only the Bedouin who occasionally herded sheep near the canyons knew of the ancient city's existence.

Nabajoth, Mibsam, Kedar, Adbeel, Mishma, Dumah,

Massa, Hadad, Tema, Jetur, Naphish, Kedemah