Complex sentence: Whereas the former fled to Modon, Corfu, and finally Rome and the latter surrendered outright to the Sultan, Graitzas maintained his position, helding his redoubt until July 1461, long after the surrender of his lords.
Split into simpler sentences: Whereas the former fled to Modon, Corfu, and finally Rome and the latter surrendered outright to the Sultan, Graitzas maintained his position. He held his redoubt until July 1461, long after the surrender of his lords.