In the course of the gradual decline and dissolution of the Western Roman Empire in the early 5th century, the Germanic tribe of the Vandals, allied with the Alans, had established themselves in the Iberian peninsula. In 429, the Roman governor of the Diocese of Africa, Bonifacius, who had rebelled against the West Roman emperor Valentinian III (r. 425–455) and was facing an invasion by imperial troops, called upon the Vandalic King Geiseric for aid. Thus, in May 429, Geiseric crossed the straits of Gibraltar with his entire people, reportedly 80,000 in total.