Investment (military)

Reconstructed section of the investment fortifications at Alesia

Investment is the military process of surrounding an enemy fort (or town) with armed forces to prevent entry or escape.^[1]^[2] It serves both to cut communications with the outside world and to prevent supplies and reinforcements from being introduced.

A contravallation is a line of fortifications, built by the attackers around the besieged fortification facing towards an enemy fort to protect the besiegers from sorties by its defenders and to enhance the blockade.^[3]^[4] The contravallation can be used as a base to launch assaults against the besieged city or to construct further earthworks nearer to the city.

A circumvallation may be constructed if the besieging army is threatened by a field army allied to an enemy fort. It is a second line of fortifications outside the contravallation that faces away from an enemy fort. 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.^[5]

Lines of contravallation and circumvallation generally consist of earthen ramparts and entrenchments that encircle the besieged city.

^ invest Merriam-Webster
^ "4. Milit. The surrounding or hemming in of a town or fort by a hostile force so as to cut off all communication with the outside; beleaguerment; blockade" (Oxford English Dictionary: investment, n. Second edition, 1989; online version December 2011. Entry/99052. Earlier version first published in New English Dictionary, 1900).
^ ^{[verification needed]} Oxford English Dictionary: circumvallation, n. Second edition, 1989; online version December 2011. Entry/33402. Earlier version first published in New English Dictionary, 1889.
^ Harry Pratt Judson (1961), Caesar's Army: A Study of the Military Art of the Romans in the Last Days of the Republic, New York: Biblo & Tannen, p. 87, ISBN 9780819601131, If an attempt at relief from without was to be feared, another line of works must be created, outside the first, and facing outwards. In modern warfare this latter line is called the circumvallation, and the inner one the contravallation.
^ ^{[verification needed]} Oxford English Dictionary: contravallation, n. Second edition, 1989; online version December 2011. Entry/40491. Earlier version first published in New English Dictionary, 1893.

[1] vest Merriam-Webster

[2] "4. Milit. The surrounding or hemming in of a town or fort by a hostile force so as to cut off all communication with the outside; beleaguerment; blockade" (Oxford English Dictionary: investment, n. Second edition, 1989; online version December 2011. Entry/99052. Earlier version first published in New English Dictionary, 1900).

[3] {[verification needed]} Oxford English Dictionary: circumvallation, n. Second edition, 1989; online version December 2011. Entry/33402. Earlier version first published in New English Dictionary, 1889.

[4] Harry Pratt Judson (1961), Caesar's Army: A Study of the Military Art of the Romans in the Last Days of the Republic, New York: Biblo & Tannen, p. 87, ISBN 9780819601131, If an attempt at relief from without was to be feared, another line of works must be created, outside the first, and facing outwards. In modern warfare this latter line is called the circumvallation, and the inner one the contravallation.

[5] {[verification needed]} Oxford English Dictionary: contravallation, n. Second edition, 1989; online version December 2011. Entry/40491. Earlier version first published in New English Dictionary, 1893.

[1]

[2]

[3]

[4]

[5]