The French Hugh IV of Burgundy spent the winter of 1248–49 in Achaea. He was on the way towards Cyprus where the participants of Louis IX of France's crusade against Egypt were assembling. William decided to join the crusade, and mustered 400 knights and armed a fleet of 24 ships before he left for Cyprus together with Hugh in May 1249. On the way he sent 100 knights to Rhodes, an island that the Genoese recently conquered from the Nicaeans, to strengthen its defence. From Cyprus William accompanied Louis to Egypt and remained with him until the end of the abortive military campaign. As a reward, Louis granted him the right to mint coins in the style of the French . William returned to Achaea in May 1250. During the following five peaceful years, Achaea was the dominant power of Frankish Greece as most lesser Frankish rulers acknowledged William as their overlord.