 As in Africa , dynastic struggles in Ostrogothic Italy provided an opportunity for intervention . The young king Athalaric had died on 2 October 534 , and a usurper , Theodahad , had imprisoned queen Amalasuntha , Theodoric 's daughter and mother of Athalaric , on the island of Martana in Lake Bolsena , where he had her assassinated in 535 . Thereupon Belisarius with 7 @,@ 500 men invaded Sicily ( 535 ) and advanced into Italy , sacking Naples and capturing Rome on 9 December 536 . By that time Theodahad had been deposed by the Ostrogothic army , who had elected Vitigis as their new king . He gathered a large army and besieged Rome from February 537 to March 538 without being able to retake the city . 
