Constantine's share of the Empire consisted of Britain, Gaul, and Spain, and he commanded one of the largest Roman armies which was stationed along the important Rhine frontier. He remained in Britain after his promotion to emperor, driving back the tribes of the Picts and securing his control in the northwestern dioceses. He completed the reconstruction of military bases begun under his father's rule, and he ordered the repair of the region's roadways. He then left for Augusta Treverorum (Trier) in Gaul, the Tetrarchic capital of the northwestern Roman Empire. The Franks learned of Constantine's acclamation and invaded Gaul across the lower Rhine over the winter of 306–307 AD. He drove them back beyond the Rhine and captured Kings Ascaric and Merogais; the kings and their soldiers were fed to the beasts of Trier's amphitheatre in the adventus (arrival) celebrations which followed.