Investment (military)

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Reconstructed section of the investment fortifications at Alesia AlesiaFortifications.JPG
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 circumvallation 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 resulting fortifications are known as "lines of circumvallation".[ citation needed ] Lines of circumvallation generally consist of earthen ramparts and entrenchments that encircle the besieged city. The line of circumvallation can be used as a base to launch assaults against the besieged city or to construct further earthworks nearer to the city.

A contravallation may be constructed if the besieging army is threatened by a field army allied to an enemy fort. [5] It is a second line of fortifications outside the circumvallation that faces away from an enemy fort. The contravallation 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. [6]


Schematic view of the circumvallation during the Siege of Groenlo in 1627 Siege of Grol (Groenlo) 1627 - Grolla Obsessa et Expugnata (J.Blaeu).jpg
Schematic view of the circumvallation during the Siege of Groenlo in 1627

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 and contravallation to defeat the Gauls under their chieftain, Vercingetorix, at the Siege of Alesia in September 52 BC.

Middle Ages

Another example from the pre-modern period is the siege of Siege of Constantinople (717–718).

The caliph of the Umayyad Empire took advantage of the violent anarchy in the Byzantine Empire to prepare a huge host, comprising more than 100,000 troops and 1,800 ships, to take them to the Byzantine capital, Constantinople. Upon arriving outside the city's Theodosian walls, the Arab host had some knowledge that Emperor Leo III the Isaurian had allied with Bulgaria under Khan Tervel, and so, in preparation for the Bulgarian army, built a set of stone walls against the city and against the countryside, with the Arab camp in between. [7]

King Pepin the Short of Francia built a number of fortified camps during his Siege of Bourbon (761) to surround the town completely. [8] He built a complete set of lines of circumvallation and contravallation during the Siege of Bourges (762). [9]

Modern era

The basic objectives and tactics of a military investment have remained the same in the modern era. During the Second World War, there were many sieges and many investments. One of the best-known sieges of the war, which demonstrated the tactical use of investment, was the Siege of Stalingrad. During the first half of the siege, the Germans were unable to fully encircle the city and so the Soviets got men and supplies in across the Volga River. During the second half of the battle, the complete investment of Stalingrad by the Soviets, including airspace, which prevented the construction by the Germans of an adequately large airbridge, eventually forced the starving Germans in the city to surrender.

In modern times, investments and sieges of cities are often combined with intensive shelling and air strikes.

See also

Related Research Articles

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Siege of Breda (1637) Siege in 1637, part of the Eighty Years War

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Fortified region of Belfort

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Siege of Badajoz (1658) 1658 battle during the Portuguese Restoration War

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Siege of Dunkirk (1658)

The Siege of Dunkirk in 1658 was a military operation by the allied forces of France and Commonwealth England intended to take the fortified port city of Dunkirk, Spain's greatest privateer base, from the Spanish and their confederates: the English royalists and French Fronduers. Dunkirk was a strategic port on the southern coast of the English Channel in the Spanish Netherlands that had often been a point of contention previously and had changed hands a number of times. Privateers operating out of Dunkirk and other ports had cost England some 1,500 to 2,000 merchant ships in the past year. The French and their English Commonwealth allies were commanded by Marshal of France Turenne. The siege would last a month and featured numerous sorties by the garrison and a determined relief attempt by the Spanish army under the command of Don Juan of Austria and his confederate English royalists under Duke of York and rebels of the French Fronde under the Great Condé that resulted in the battle of the Dunes.


Counter-castles were built in the Middle Ages to counter the power of a hostile neighbour or as a siege castle, that is, a fortified base from which attacks could be launched on a nearby enemy castle.

The Siege of Bourges was a Frankish siege of the Aquitanian fortress town of Bourges in 762 during the Aquitanian War. The Frankish army under King Pepin the Short invested the fort with lines of circumvallation, contravallation and siege engines. The walls were breached and the fort taken. Count Chunibert of Bourges swore his loyalty to Pepin along with his Gascon levies and their families. Pepin appointed several counts of his own to garrison the place and the Frankish army went on to besiege Thouars.


  1. invest 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. Definition of circumvallation
  4. Oxford English Dictionary: circumvallation, n. Second edition, 1989; online version December 2011. Entry/33402. Earlier version first published in New English Dictionary, 1889.
  5. Definition of contravallation
  6. Oxford English Dictionary: contravallation, n. Second edition, 1989; online version December 2011. Entry/40491. Earlier version first published in New English Dictionary, 1893.
  7. Petersen 2013, pp. 703–708.
  8. Petersen 2013, p. 729.
  9. Petersen 2013, pp. 730–731.