The word cannon comes from the Greek kanun, meaning a tube. One early surviving cannon was an octagonal tube with a round bore. It had a breech block hammered in to place during casting. Cuprum and latten, both forms of brass, were used to make guns. But soon it was clear that cast iron was the best material. At first cannons were either placed on a mount to point them upwards or tied to a wooden board in order to tip the weapon and aim it by placing wedges underneath. In the fifteenth century one finds trunnions (wheeled platforms) in use. Cannons were loaded either by a mobile chamber or thunder-box, or else at the breech. The chamber was filled with gunpowder and a heated touch applied to the hole in the tube or the touch-hole. The chamber was closed with a bung of soft wood to act as a wad between the charge and the shot. The bung would pop out like a cork, the idea being that the chamber itself should not explode. The mobile chamber was placed in the breech and clamped with an iron rod, then packed with tow. By the middle of the fifteenth century some very large cannons were being manufactured.
Roman Artillery II
The practical Romans had only to make one or two refinements to Greek models and then put the machines to use. Artillery machines came in several different sizes, the determining factor being the size of the bolt to be shot or the weight of the stone to be projected. Vitruvius explains how this affects the proportions in manufacturing catapultae and ballistae, including a ready-reckoner relating weight of the stones to the proportions of the machine “so that those who are not skill ed in geometry may be prep a red beforehand and not be delayed in thinking the matter through at a time of danger” (De Architectura 10. 10.-11). The bolts or stones were placed in the central channel, and the bowstring was pulled back onto the trigger, the only difference being that the bowstrings for stone-throwing machines were broader, approximating to a sling that encompassed the stone ball, with a loop at the back for the trigger.
Roman Artillery I
Late Roman artillery at the Saxon shore.
The legionaries were well equipped with artillery: a figure of around 60 machines per legion is found in both Josephus (Jewish War 3.166) and Vegetius (2.25). The machines were of various sizes: Trajan’s Column shows both man-portable boltthrowers (manuballistae, cheiroballistrae) and those mounted on a mule-drawn carriage (carroballistae) (Scenes 65-66). Range and accuracy were impressive: at Hod Hill in Dorset, a hill-fort probably captured by Legio II Augusta in ad 43, 17 bolt-heads have been found, still embedded in the chalk where they struck. Eleven had hit Hut 37 (dubbed by archaeologists the “Chieftan’s Hut”), landing in a ten-meter circle, including four that landed in a three-meter circle, all from an estimated range of 170 meters. Of the six other shots it is likely that some at least were initial ranging shots, from which the firers corrected their aim. A reconstructed cheiroballistra has achieved similar results. Although crucial in sieges and assaults, artillery was used in field battles too: at Cremona in ad 69, an “enormous ballista,” of the Fifteenth Legion threw “huge” stones at the Flavian army; only by disguising themselves with the shields of fallen Vitellian troops did two bold individuals put it out of action, by cutting the twisted cord springs which provided its torsion (Tacitus, Hist. 3.25) – a key vulnerability of such machines.