An infantry square, also known as a hollow square, was a historic close order formation used in combat by infantry units, usually when threatened with cavalry attack. To deploy its weapons effectively, a traditional infantry unit would generally form a line; but the line was vulnerable to more nimble cavalry, which could sweep around the end of the line, or burst through it, and then attack the undefended rear or simply sweep along the line attacking the individual footsoldiers successively. By arranging the unit so that there was no undefended rear or flank, an infantry commander could organise an effective defense against cavalry attack. With the development of modern firearms and the demise of cavalry, the square formation is now considered obsolete.
A depiction of a Napoleonic-era British infantry square at the Battle of Quatre Bras, Belgium, 1815.
Infantry of the French Revolutionary Army in square formation, under attack by Chouan rebels at the Battle of Rocher de La Piochais, 21 December 1795.
The charge of the French Cuirassiers at the Battle of Waterloo against a British square.
Egyptian Mamluk cavalry charges a French infantry square during the Battle of the Pyramids, 1798.
A close order formation is a military tactical formation in which soldiers are close together and regularly arranged for the tactical concentration of force. It was used by heavy infantry in ancient warfare, as the basis for shield wall and phalanx tactics, to multiply their effective weight of arms by their weight of numbers. In the Late Middle Ages, Swiss pikemen and German Landsknechts used close order formations that were similar to ancient phalanxes.
Close order formation: Greek hoplites marching in phalanx formation.
In close formation, Swiss pikemen confront Holy Roman imperial cavalry at the Battle of Dornach, 1499.
Prussian infantry in close order linear formation attack at the Battle of Hohenfriedberg, 1745.