During the first half of the 20th century some scholars developed certain theories concerning the Byzantine origins of El Greco's style. Professor Angelo Procopiou had asserted that, although El Greco belongs to Mannerism, his roots were firmly in the Byzantine tradition. According to art historian Robert Byron "all Greco's most individual characteristics, which have so puzzled and dismayed his critics, derive directly from the art of his ancestors". On the other hand, Cossío had argued that Byzantine art could not be related to El Greco's later work.