The most effective way to break a square was not direct cavalry attack but the use of artillery, particularly firing canister shot, which could massacre the tightly packed infantry of the square. To be truly effective, such artillery fire had to be delivered at close range. A 20 m wide infantry square was a small and difficult target for field artillery firing from within or just in front of its own army's lines, typically at least 600 m away, a range at which most rounds could then be expected to miss. Thus, attackers would usually try to deploy horse artillery accompanying the cavalry. The presence of the cavalry would cause the infantry to form square, but the closely packed infantrymen would then become targets for the artillery since the cohesion of the square would break under their fire, making it much easier for the cavalry to press home the attack.