And first we must call attention to the fact that two classes of vessels appear to have been employed, distinguished by the name of "Aphract," unfenced, or "Cataphract," fenced, according as the rowers of the upper tier were protected or exposed. Both classes were decked and floored, but the "Aphract" class carried their decks and flooring lower than the "Cataphract," so that in them the rowers of the upper tier were visible above the side of the vessel; … [F]rom the time of the invention by the Thasians of this system, all the larger vessels of war used by both Greeks and Romans were Cataphract. In the Cataphract trireme, the space allowed for each oarsman was, according to [B.] Graser, eight square feet per man, and this proportion was observed in the larger vessels up to the octireme.