The End of the Roman Frontier in Arabia
The Roman military presence in Arabia began to decline in the mid-400s when forces were diverted to other threatened frontiers. In the early 500s, Justinian turned over the defense of the southeastern frontier to the Ghassanids, a Christian Arab tribe. Around AD 530, the troops were withdrawn and the limes Arabicus ceased to exist. The forts of el-Lejjun, Khirbet el-Fityan, Rujm Beni Yasser, Qasr Bshir, and Da'janiya were abandoned at this time. The numerous watchtowers provide no evidence of occupation in the sixth or early seventh centuries. At least by the early 600s, the fortified frontier system in Palestine and Transjordan no longer existed. This withdrawal of defenses paved the way for the eventual Muslim conquest of the region in the 600s.