Wren's "Tracts" on Architecture and Other Writings is the first scholarly examination of the theoretical work of one of the most important architects of early modern Europe. From his study of ancient buildings, he posited a new version of the origins and development of the Classical style, thereby becoming one of the first to challenge theoretical principles of architecture that had been upheld since the Renaissance. Rejecting the idea of beauty as absolute and innate, Wren formulated an empirical definition, based on visual perception and custom.