Whatever the ancient Balista may have been, the word in mediaeval Latin seems always to mean some kind of crossbow.  The heavier crossbows were wound up by various aids, such as winches, ratchets, etc.  They discharged stone shot, leaden bullets, and short, square-shafted arrows called quarrels, and these with such force we are told as to pierce a six-inch post (?).  But they were worked so slowly in the field that they were no match for the long-bow, which shot five or six times to their once.  The great machines of this kind were made of wood, of steel, and very frequently of horn;[3] and the bow was sometimes more than 30 feet in length.  Dufour calculates that such a machine could shoot an arrow of half a kilogram in weight to a distance of about 860 yards.

The Trebuchet consisted of a long tapering shaft or beam, pivoted at a short distance from the butt end on a pair of strong pyramidal trestles.  At the other end of the shaft a sling was applied, one cord of which was firmly attached by a ring, whilst the other hung in a loop over an iron hook which formed the extremity of the shaft.  The power employed to discharge the sling was either the strength of a number of men, applied to ropes which were attached to the short end of the shaft or lever, or the weight of a heavy counterpoise hung from the same, and suddenly released.

[Illustration:  Mediaeval Artillery Engines.  Figs. 1, 2, 3, 4, 5, Chinese; Figs. 6, 7, 8, Saracenic:  the rest Frank.]

Supposing the latter force to be employed, the long end of the shaft was drawn down by a windlass; the sling was laid forward in a wooden trough provided for it, and charged with the shot.  The counterpoise was, of course, now aloft, and was so maintained by a detent provided with a trigger.  On pulling this, the counterpoise falls and the shaft flies upwards drawing the sling.  When a certain point is reached the loop end of the sling releases itself from the hook, and the sling flies abroad whilst the shot is projected in its parabolic flight.[4] To secure the most favourable result the shot should have acquired its maximum velocity, and should escape at an angle of about 45 deg..  The attainment of this required certain proportions between the different dimensions of the machine and the weight of the shot, for which, doubtless, traditional rules of thumb existed among the mediaeval engineers.

The ordinary shot consisted of stones carefully rounded.  But for these were substituted on occasion rough stones with fuses attached,[5] pieces of red-hot iron, pots of fused metal, or casks full of Greek fire or of foul matter to corrupt the air of the besieged place.  Thus carrion was shot into Negropont from such engines by Mahomed II.  The Cardinal Octavian, besieging Modena in 1249, slings a dead ass into the town.  Froissart several times mentions such measures, as at the siege of Thin l’Eveque on the Scheldt in 1340, when “the besiegers by their engines