One of the classic forms of
heavy infantry. Just like it sounds, it consists of a wall of overlapping
shields designed to protect the soldiers behind them from the enemy.
The most obvious advantage of being behind a shield is the protection it offers from missiles, but its value close in was also significant. While vulnerable to
heavy cavalry, it was very hard to break a shield wall with anything else save another shield wall. And combat between two shield walls was about as ugly as it ever got.
Historically, the most famous shield walls were those of the
Greeks (whose
Hoplites used a variation with very long
spears), the
Roman Legions, and the
Vikings.
Shield wall tactics, although made obsolete in war by the gun, are still used today by
riot police around the world. In fact, the standard
riot shield is little changed from the
scutum used by the
Roman legions, save for the fact that they're made of modern material.