Much of his work was based on the classical style of Greece and Rome. In his 1924 autobiography, Louis Sullivan, one of the leading architects from the Chicago School but one who had enjoyed difficult relations with Burnham over an extended period of time, criticised Burnham for what Sullivan viewed as his lack of original expression and dependence on Classicism.[13] Sullivan went on to claim that "the damage wrought by the World's Fair will last for half a century from its date, if not longer"[14]—a sentiment edged with bitterness, as corporate America of the early 20th century had demonstrated a strong preference for Burnham's architectural style over Sullivan's.