the next year, they conquered all of Sicily, ending the Islamic Emirate of Sicily. In 1074, the Byzantine Emperor Michael VII sent an envoy to Robert offering the hand of his son Constantine to Robert's daughter Helena. Guiscard accepted the offer and sent his daughter to Constantinople. However, in 1078, Michael was overthrown by Nicephorus Botaneiates, an event that destroyed any chances Helena had for the throne. This gave Robert a motive to invade the empire claiming his daughter had been mistreated; however, his intervention was delayed by a revolt in Italy. Robert conscripted all men of a fighting age into the army, which he refitted. Meanwhile, he sent an ambassador to the Byzantine court with orders to demand proper treatment for Helena and to win over the Domestic of the Schools, Alexios. The results of these attempts remain unknown, but the ambassador fell under Alexios's charm and as he was returning to Italy, he heard of Alexios's successful coup against Botaneiates, by which he became Alexios I Komnenos. When the ambassador returned, he urged Robert to make peace, claiming that Alexios wanted nothing but friendship with the Normans. Robert had no intention of peace; he sent his son Bohemond with an advance force towards Greece and Bohemond landed at Aulon, with Robert following shortly after. Prelude The Norman fleet of 150 ships including 60 horse transports set off towards the Byzantine Empire at the end of May 1081. The army numbered 15,000 men, including about 1,300 Norman knights. The fleet sailed to Avalona in Byzantine territory; they were joined by several ships from Ragusa, a republic in the Balkans who were enemies of the Byzantines. Robert soon left Avalona and sailed to the island of Corfu, which surrendered because of a small garrison. Having won a bridgehead and a clear path for reinforcements from Italy, he advanced on the city of Dyrrhachium, the capital and chief port of Illyria. The city was well defended on a long, narrow peninsula running parallel to the coast, but separated by marshlands. Guiscard brought his army onto the peninsula and pitched camp outside the city walls. However, as Robert's fleet sailed to Dyrrhachium, it was hit by a storm and lost several ships. Meanwhile, when Alexios heard that the Normans were preparing to invade Byzantine territory, he sent an ambassador to the Doge of Venice, Domenico Selvo, requesting aid and offering trading rights