According to ancient sources, the earliest reference to Tarasis dates back to 464, when he put his hands on some letters written by Aspar's son, Ardabur, which proved that the son of the "magister militum" had incited the Sassanid King to invade Roman territory, promising to support the invasion. Through these letters, which Tarasis gave to Leo, the Emperor could dismiss Ardabur, who at the time was "magister militum per Orientem" and "patricius", thus reducing Aspar's influence and ambition. As reward for his loyalty, which Leo praised to Daniel the Stylite, Tarasis was appointed "comes domesticorum", an office of great influence and prestige. This appointment could mean that Tarasis had been a "protector domesticus", either at Leo's court in Constantinople, or attached at Ardabur's staff in Antioch.