John, Duke of Barcaina
John, Duke of Barcaina (also John, Duke of Barca; Greek: Ἰωάννην τὸν Βαρκαίνης στρατηγὸν; d. May 640) was a Byzantine general (magister militum) and dux of the Libyan Pentapolis who died defending Egypt during the Arab conquest. There are a few mentions of him in ancient sources, but whether they all refer to the same person or not is debated.