In later times larger vessels were invented for special purposes—four-banked (_quadriremes_), five-banked (_quinquiremes_), and so on, even up to one of forty banks; but as we are unable to understand how it was possible for more than five or six tiers of oars to be operated, we may leave these extraordinary galleys to special students.[4] The structure of these vessels gave them the greatest strength combined with lightness. They had very strong keels and stems, the latter peculiarly braced; and along their sides ran waling-pieces, or fore-and-aft bracing timbers, the lowermost curving inward forward, until they met in front of the stem at the water-line, where they were braced by massive timbers, and prolonged into a sharp three-toothed spur, of which the middle tooth was the longest, reaching out perhaps ten feet. This was covered with metal, usually bronze, and formed the _beak_. “Above it, but projecting less beyond the stem-post, was the _procmbolion_, or second beak, in which the prolongation of the upper set of waling-pieces met. This was generally fashioned into the figure of a ram’s head, also covered with metal.... These bosses, when a vessel was rammed, completed the work of destruction begun by the sharp beak at the water-level, giving a racking blow which caused it to heel over and so eased it off the beak, releasing the latter before the weight of the sinking vessel could come upon it.” [Illustration: HAMILCAR’S “STAIRWAY OF THE GALLEYS,” AT CARTHAGE.] The stem was often carried up into a curving ornament called the _acrostolion_, beneath which was a stout-walled deck-space for sailors or the fighting-men to do their work; and the stern-post similarly supported a lofty, richly ornamented structure (_aplustron_), arching over the officers’ quarters. Platforms extended up and down the center of the ship between the rowers; and over their heads was a deck having walls or bulwarks where the fighting-men and their various “engines” stood. In addition to this an external defended gallery for soldiers and boarders usually ran along the outside of the bulwarks above the oars; and awnings of rawhide were stretched over all to ward off grappling-irons. It must not be forgotten, however, that these galleys also had three pole-masts, and certain sails—probably a huge split lug, with possibly a square topsail on the mainmast, while the fore- and mizzenmasts carried lateens. At the top of each stick was a round, protected cage filled with archers and slingers—the prototype of our “military mast.”