Following an appeal from the Byzantine emperor for foreign military assistance to defeat the Seljuk Turks, it took only a few years from the pope’s first call to arms of 1095 for invading Christian European armies to seize Jerusalem. European-run statelets were set up in quick succession throughout the Levant – the Kingdom of Jerusalem, the Counties of Tripoli and Edessa, and the Principality of Antioch. One of the Christian lords, Baldwin, was crowned King of Jerusalem on Christmas Day 1100, and it was under his rule that the Crusaders began to realize the benefit of controlling the Transjordanian land route from Syria into Egypt and Arabia, in order to stand between the Muslim power bases in Damascus and Cairo and to be able to harass Muslims making the pilgrimage to Mecca.
In 1107, the threat of attack by Baldwin’s army persuaded a Seljuk force to flee their stronghold in Petra, and persistent harrying over a decade or more in the area around Ajloun successfully played havoc with established trade patterns in the region. In 1115, Baldwin crossed the Wadi Araba from Hebron with the intention of fully incorporating Transjordan into the Crusader realms, and began construction of a large castle at modern Shobak, which he named Le Krak de Montreal (“Fortress of the Royal Mountain”). Establishment of a string of Crusader possessions soon followed, at Aila (Aqaba), Wu’ayra and Habees at Petra, and Tafileh. However, the Lordship of Oultrejourdain, as it came to be known, was far from impregnable, and infiltration across the River Jordan by a Muslim raiding party in 1139 seems to have persuaded Paganus the Butler, by then the effective ruler, to move his power base northwards from Shobak. Construction of the massive fortress at Karak began in 1142, and twenty years later, with the addition of another citadel at Ahamant (possibly Amman), Crusader-controlled territory in Transjordan extended from the River Zarqa to the Red Sea, and from the Jordan Valley to the desert.
Such power was short-lived, however. Between 1169 and 1174, the Karak headquarters underwent four sieges, managing to survive partly because the opposing Muslim armies were divided. By 1174, though, Salah ad-Din had united the Muslim forces and began methodically to oust the Crusaders from Transjordan. Karak withstood two more sieges during 1183, but the tide was turning: the Latin armies were much depleted, and their young king, Baldwin IV, was dying of leprosy. In 1187, at Hattin near Tiberias, they were roundly defeated by Salah ad-Din, who soon after took Jerusalem. Wu’ayra and the great prize, Karak itself, capitulated in late 1188, and Shobak – the last Transjordanian possession – fell in the spring of 1189. The Europeans struggled on, but a century later the entire Holy Land was once again under Arab rule.