An infantry square is a battle tactic of infantry when faced with cavalry. It was a formation described by Plutarch and used by the Romans, a development of an earlier circular formation. It was revived in the 14th century as the schiltron, in the 15th century as the pike square and again in the 17th century for mass, musket-armed forces. It was widely used in the Napoleonic War and remained a valuable manoeuvre against irregular cavalry forces throughout the 19th century.
The infantry form a hollow square, facing out on all sides in two, three, or more ranks with fixed (socket) bayonets. Generally, a battalion was the smallest force to drill in forming a square. The unit's colours, commander, and a reserve force are positioned in the centre of the square. If the square maintained cohesion, cavalry had almost no chance of breaking it.
Once formed in a square the infantry would volley fire at each cavalry charge, either by file or by rank. In successful actions, the infantry would often withhold fire until the charging horses were as close as twenty paces — eventually a wall of horse and human bodies presented an even greater obstacle to a successful charge. Undisciplined or early fire could fatally weaken a square.
Cavalry attacking a square would, if lacking artillery support, attack the corners of the square — the weakest points — in close waves. Feints and false attacks to reduce the volume of fire would also be used.
While it was vital for squares to stand firm in the face of a charge, they were not static formations. Astute commanders could, in suitable terrain, manoeuvre squares to mass fire and even trap cavalry, as Napoleon and Kléber managed against the Turks at Mount Tabor in 1799. Similarly squares could be arranged in a checker-board formation to give supporting fire as cavalry broke around a single square.
At the battle of Waterloo the four-rank squares of the Allied forces withstood eleven unsupported cavalry charges. At Lützen, despite infantry and light artillery support, green French troops easily repulsed an Allied charge. Similarly impressive infantry efforts were seen at Auerstädt, Jena, Pultusk, Krasnoe, and a number of other battles. If a square was broken, like at Rio Seco or Quatre Bras, the infantry could suffer many casualties — although brave and well-disciplined infantry could recover even from a break-through.
