As the Roman Empire declined in the 5th century AD, the Noricum region was exposed to recurring campaigns of Germanic tribes, whereupon the population retired to hilltop settlements. In 408 Visigoth troops under King Alaric I entered Noricum from Italy across the Carnic Alps and forged an alliance with the Roman commander Stilicho, who as a result was deposed and executed for high treason (August 408). From 472 Ostrogoth and Alemannic forces campaigned in Noricum, which became a province of Odoacer's Kingdom of Italy in 476 and of the Ostrogothic Kingdom from 493. On the death of King Theoderic the Great in 526, the Italian kingdom finally collapsed and the East Roman Byzantine empire under Justinian I temporarily conquered the Noricum region in the course of the Gothic War of 535 to 554.