When paddles were made larger to suit hulls of larger dimensions, it may fairly be assumed that a winch turned by several men was used, and that the power was transmitted to the axle of the paddle by means of an endless rope. But soon it occurred to the shipowners that animals might be used to produce the power instead of men. Horses or oxen were made to drive a turntable or capstan, to work in a cage after the fashion of white mice in their cylinders, or on a moving floor which imparted its motion to an axle connected by an endless rope with the axle of the paddle. Such boats, deriving their power from animals, were built by the Romans, were in use in the early centuries of the Christian era, and were not unknown in the nineteenth century in Britain and the United States. [Illustration: PRIMITIVE PADDLE-BOATS. _From Valturius’ “De Re Militari,” 1472._] One of the earliest authentic records of a vessel fitted with paddle-wheels is to be found in Robertus Valturius’ “De Re Militari,” published in 1472, wherein are pictures[2] of two boats, one of which has five pairs of paddle-wheels, and the other one pair. Modern engineers know by experience that if two wheels be placed one behind another--and in the early days of steam navigation several boats were equipped with two pairs of paddle-wheels--the hinder wheels, having to work in disturbed and moving water, are practically useless. But at the time of which Valturius writes the wheels were so small, the number of revolutions were so few, and the propelling power they exerted so slight, that no wheel was likely to have its efficiency much interfered with by any number of wheels in front of it. The wheels had four paddles each, and were revolved by cranks on their axles, the cranks of the ten-wheeled boat being connected by a rope to give uniform action. [2] The designs have been attributed to Matteo de’ Pasti, who lived at the court of Malatesta (d. 1464).