in the naval architecture of the ancients, is a word used to express such of their galleys as had three, four, five, or more tiers of rowers, seated at different heights; they were distinguished by this term from the monocrota, or those which had only single rows of oars. The number of rows of rowers in the polycrota galleys has given occasion to some to suppose those vessels of such a height from the water as is scarce credible. Commentators are not at all agreed upon the construction of these vessels.