In 1061, after a successful campaign against the Byzantines in the south of Italy, the Norman Robert Guiscard invaded the Emirate of Sicily and captured Messina. After a prolonged campaign, the Normans completed the conquest of Sicily by 1091. The Norman Kingdom of Sicily developed a vibrant culture, and became a gateway that opened the world of Greek philosophy and Muslim science to Western Europe. (Later the Normans went on to sack and occupy Constantinople itself in 1204 during the Fourth Crusade).