The Pike Square was a military tactic developed by the Swiss Confederacy during the 15th century for use by its light infantry. It was used to devestating effect at the Battle of Nancy against Charles the Bold of Burgundy in 1477, when the Swiss defeated a smaller but more powerful armored cavalry force. The battle is generally seen as one of the turning points that led to the downfall of armored knights and the feudal system.

From approximately the 10th century to the 15th century, armored knights on horseback dominated European military and political affairs, and were rarely defeated in military engagements. (The English tactic of avoiding wide-open fields that allowed mass cavalry charges and using masses of archers using longbows instead of crossbows showed the vulnerability of cavalry and led to devastating losses at the battles of Crécy in 1346 and Agincourt in 1415. However, armies have to be able to fight on ground not of their own choosing, and the longbow was a difficult weapon to master, so armored knights remained the master of most battlefields.)

In response to the threat posed by the Burgundians, the Swiss developed a tactic that could be used by mobile, lightly armored soldiers carrying only a long, steel-tipped pole for defence. However, the tactic depended on well trained and drilled troops who could move in unison while in close formation. While use of pointed sticks to fend off cavalry was common in the 15th century, such barricades were usually fixed in position.

A pike square generally consisted of about 100 men in a 10×10 formation. While on the move, the pike would be carried vertically. However, the troops were drilled to be able to point their pike in any direction while stationary, with the men in the front of the formation kneeling to allow the men in the center or back to point their pike over their head. While stationary, the staff of the pike could be butted against the ground, giving it resistance against attack. Squares could be joined together to form a battle line. If surrounded, pikes could still be pointed in all directions. A well drilled square could literally turn on a dime, making it difficult to outmaneuver on horseback.

Charles did not believe that a force even twice his size on foot without archers could possibly pose him any threat. However, Charles and his forces found the pike square impossible to penetrate on horses, and dangerous to approach on foot. When threatened, the square could point as many pikes as possible at the enemy forces, and merely move inexorably towards its target. At Nancy, the Swiss routed the Burgundians, and Charles himself died in the battle.

The pike square dominated European battlefields and drove tactics well into the 19th century. When muskets became common weapons, the pikes were replaced by muskets with bayonets to the same effect. It was only at the Battle of Shiloh that accurate long range rifled muskets made mass bayonet charges impossible. (See infantry square.)