The 'bireme,' or two-banked vessel, does not appear in Homer. But, as we have seen, it was probably in existence before Homer's time. If of Egyptian parentage, it was adapted for use on the Mediterranean waters by the shipwrights of Sidon or Tyre. It is a curious reflection that this remarkable evolution of banked vessels should, so far as we can judge, have occupied about two thousand years; the curve, if we may use the expression, of development rising to the highest point in the useless Tesseraconteres of Ptolemy, and after Actium declining to the dromons and biremes of the Byzantine Emperor Leo, and finally subsiding into the monocrota or one-banked vessels, the galleys of mediaeval times. The problem which taxed the ingenuity of those early shipwrights was briefly this, how to get greater means of propulsion by increasing the number of oars, without such increase in the length of the ship as would, by increased weight, neutralise the advantage and still further diminish that facility in turning which was of the greatest moment to the ancient war-vessel. Galleys with fifty oars on either side had already been constructed,[2] and all the speed that a hundred pairs of hands could give had been obtained, when the invention of the bireme exhibited the means of nearly doubling the power without much increasing the weight to be moved, since but little additional height or breadth was required. [2] Perhaps even with a hundred, if [hekathozygos] is to be taken literally. The normal adjustment of the horizontal space between the oarsmen was then, as it is now, regulated by that canon of the ancient philosopher, 'Man is the measure of all things.' Twice the man's cubit gives room for his legs when in a sitting posture. Hence the two-cubit standard ([schema dipechaikhon]) which is referred to by Vitruvius as the basis of proportion in other constructions besides ships and boats. Given this as the interscalmium (space between the thowls) or distance between points at which the oars in the same tier were rowed, it is clear that the rowing space of a vessel's side would be, for a penteconter, or twenty-five a side, seventy-five feet, and for a hecatonter, if there ever was such a thing, 150 feet. To this must be added the parts outside the oarage space ([parexeireshia]), for the bows ten feet, and something more, say twelve feet, for the stern. So that a penteconter would be a long low galley of about ninety-seven feet in length. The new invention nearly doubled the number of oars without increasing the length of the oarage space.