The Excubitors were founded in c. 460 as an imperial guard units by the Byzantine emperor Leo I the Thracian. The 300-strong unit, originally recruited from among the warlike mountain tribe of the Isaurians, replaced the older Scholae Palatinae as the main imperial bodyguard. The Excubitors remained an active military unit for the next two centuries, although, as imperial bodyguards, they did not often go on campaign. Their commander, the Count of the Excubitors, soon acquired great influence. Justin I was able to use his position to rise to the throne in 518, and henceforth the Counts of the Excubitors were among the main political power-holders of their day; two more, Tiberius II Constantine and Maurice, rose to become emperors in the late 6th century.