_The Trebuchet._--Another force was called into play for medieval artillery. This was the counterpoise, or gravitation, and the principle upon which all large engines or "gyns" were constructed during the middle ages. A long wooden arm was pivoted in a framework so that a short and a long portion projected upon either side; to the shorter part a great weight in a swinging cradle was fixed which necessarily raised the longer arm to the vertical position. If the latter were drawn backwards and downwards the great weight was accordingly raised, and upon release the long arm would sweep upwards in a curve and project any missile attached to it. By fixing a sling of suitable length to the arm the efficiency was immensely increased (_see_ Title-page). Such was the principle of the "trebuchet," the enormous engines which carried devastation and destruction to medieval castles. The French are said to have introduced these in the twelfth century, and by the end of the thirteenth they were the most formidable siege engines of the time. [Illustration: STIRLING CASTLE, STIRLINGSHIRE.] The transition period in England between the classical weapons and the trebuchet was the twelfth century and the early part of the thirteenth. The veterans from the crusades undoubtedly introduced the torsion and tension engines, but found that the home-made article could not compete in efficiency with the Oriental examples and therefore the advent of the trebuchet was welcomed. Roughly speaking, the original balista or catapults depending upon torsion, and throwing shafts rather than balls, were not so frequently in use as those engines which depended upon tension and threw heavy stones. In the early part of the thirteenth century the balista catapult came into vogue once more; it was of the cross-bow type, and at the end of the century was called the espringale and mounted on wheels. The counterpoises used in large trebuchets weighed sometimes between 8 and 9 tons; the throwing arm was often 50 feet in length, and the engine could hurl a projectile weighing between 2 cwt. and 3 cwt. to a distance of about 300 yards. Dead horses were at times sent whirling over the battlements into a besieged town, while casks of matter of an offensive character and likely to breed pestilences were common missiles. But the chief use and purpose of the trebuchet was the smashing-up of bretasches; the pounding of the battlements and upper works to facilitate escalades; the filling up of the moat in selected places by throwing large quantities of earth, stones, etc., into it and against the walls, and, occasionally, to hurl some unfortunate envoy back again into a town or fortress when the messages he carried were distasteful to the besiegers. In a medieval MS. full directions are given for trussing a man intended for use as a projectile.