This paper examines the development of a crisis over a critical military-security issue raised by the severe earthquakes that destroyed defensive structures throughout Nur al-Din's Sultanate of Syria, the Crusader Principality of Antioch, and the County of Tripoli. The earthquakes that struck Syria in 1157 and 1170 are well documented by contemporary historians. The accounts of destruction concentrate on the collapse of many fortresses and town walls. This circumstance strongly influenced regional politics and military affairs. While the first earthquake led to an increase in tension and a rise in violence between the Crusader Kingdom of Jerusalem and the Muslim Sultanate in Syria, the destruction wrought by the 1170 earthquake forced the two sides to accept a formal peace treaty. The two case studies presented here examine the impact of earthquake destruction on decision makers in the complex international arena of medieval Syria.