Before the cannon was invented, the most common method of hurling destructive weaponry at the enemy was the catapult. Known as engines, there were three main types: the ballista, the mangonel and the trebuchet. Cannon did not appear until the 14th Century, the first recorded use being in Florence in February of 1326. From this time onwards the cannon was used on an ever-increasing scale throughout the world. By the start of the 1700s the cannon was a common weapon in European armies, with artillery units becoming of equal importance to the cavalry.
Cannon come in a range of types and sizes. Guns, mortars and howitzers are all considered to be smoothbore, which simply means that the interior of the cannon's barrel was not rifled. Rifling was the cutting of a spiral groove along the interior of the barrel, which gave the projectile spin.
Guns shot at a low trajectory and were useful for long or short range battering of fortifications. They could also be aimed with some accuracy and were therefore useful for destroying enemy cannon. Mortars, on the other hand, shot at a high trajectory, and were most suited to firing over walls. The high trajectory made them an excellent choice for raining bombs onto the enemy, and with careful planning the bomb could be timed to explode over a group of men and thus cause widespread injury. Howitzers shot at a trajectory someway between the gun and the mortar, with the added advantage that they could handle projectiles considerably larger than the other two methods.
A variety of projectiles were available, the three basic types being those that did not explode, those that did and projectiles that scattered small fragments without exploding. The size of the projectile was dictated by the size of the cannon's bore diameter. Measured in inches, the caliber size tended to closely match the weight of the iron shot at smaller calibers. A cannon with a bore of three inches would shoot an iron ball which weighed between three and four pounds. Similarly, a cannon of bore diameter nine inches would manage an iron ball of between seven and ten pounds. Eventually, the cannon came to be referred to in terms of the weight of shot they fired. A four-pounder, for example, would shoot four pound iron shot. Cannon available ranged from one-pounders right up to thirty-two-pounders, suitable for siege work.
Solid shot was any projectile which did not explode, and included cast iron spheres, bar shot and chain shot. Early artillery, such as the ballista had shown that spherical objects moved through the air much more effectively than oddly-shaped projectiles. Working on this principle, rounded stones were initially a good choice of projectile, later augmented by a thin layer of iron to improve their shape. An obvious development was to cast perfectly round balls, with varying degrees of success. Early shot featured a raised seam mark from the two part moulds used to cast the shot, though the process was quickly perfected.
Bar and chain shot were simply methods of altering the basic solid ball design, such modifications being made with the specific purpose of tearing into wooden structures, whether on land or at sea. Bar shot consisted of the two halves connected together by a short iron bar, whereas chain shot used a length of chain to achieve the same thing. While this new design was particularly good for tearing through structures or, indeed, rigging, they were of little use in maiming larger quantities of humans, and for this purpose other types of shot had to be devised.
Bombs, or explosive shells, were hollow spheres of iron into which gun powder was poured. A fuse would be inserted and then lit. By ensuring the sphere opposite the hole was slightly heavier the bomb could be encouraged to land upright, helping to avoid extinguishing the fuse. Some bombs were constructed with a short iron lip around the fuse so that it could be grasped with a pair of tongs, allowing it to be easily inserted into the cannon. (Yes, this is exactly the sort of beum encountered by Inspector Clouseau on a daily basis...)
Bombs were well suited to killing soldiers, as were scatter shot projectiles. A canister, into which was loaded small objects, would be fired into the midst of the enemy, where it would break apart and cause widespread injury. Small round shot was a favoured packing, as was grape shot, so called because it came packed in a cloth bag, wrapped around a wooden spindle, the appearance being similar to clustered grapes.
The basic cannon has, of course, long been superseded. In its time, however, the destructive capability of the cannon was considerable, and the importance of such weaponry in a wide range of battles is, as a result, undeniable.
Information gathered from various online sources and a tiny part of Hutchinson's Encyclopaedia.