Investment (military)

The circumvallation protects the besiegers from attacks by allies of the city's defenders and enhances the blockade of an enemy fort by making it more difficult to smuggle in supplies.

Thucydides notes the role circumvallation played in the Sicilian Expedition and in the Spartan siege of Plataea during the initial stages of the Peloponnesian War in 429 BC.

Julius Caesar in his Commentaries on the Gallic War describes his textbook use of the circumvallation[6] to defeat the Gauls under their chieftain, Vercingetorix, at the Siege of Alesia in September 52 BC.

[7] King Pepin the Short of Francia built a number of fortified camps during his Siege of Bourbon (761) to surround the town completely.

In modern times, investments and sieges of cities are often combined with intensive shelling, air strikes and extensive use of land and/or sea mines.