What formation did Wellington's infantry use against French cavalry attacks?

Wellington’s infantry used infantry squares against French cavalry attacks at Waterloo.

A square was a hollow formation with soldiers facing outward, typically several ranks deep, and bayonets presented on every side. Cavalry horses generally would not charge a steady square, making the formation a powerful defense against mounted troops.

Marshal Ney’s French cavalry launched repeated attacks against Wellington’s center during the afternoon of 18 June 1815. The squares held their ground, while artillery and infantry fire punished cavalry that came too close. The formation was not invulnerable: artillery, infantry, or a broken formation could defeat it. At Waterloo, however, French cavalry attacks were made without enough effective infantry and artillery support, so they failed to break the Allied line.

The famous squares were made up not only of British troops but also Dutch, Belgian, German, and other Allied units. Their discipline mattered as much as their shape: a square that panicked or opened its ranks could be overrun.