The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. 

These forts developed as a detached system where the gradual distancing of the external fortifications from the inner encirclement was observed. These forts generally maintained a low profile and were arranged in a ring around the place which was intended to protect. These were also called ‘flank-less forts’ and later as Palmerston forts as most of the forts were built during his governance.

To assist you ahead, some of the terminologies used:

Bastion: Part of the fortification wall that projects outward from the main rampart.
Enceinte: Main enclosure of the fortress consisting of a line of ramparts.
Face: The side or part of the fortress that is in-line of attack.
Glacis: An artificial gentle slope built providing an open field.
Caponier: A structure built in the moat or the ditch of the fortress to defend against enfilading fire.
Casemate: A room or a structure built in the ramparts for gun emplacement.
Counterscarp: Outer wall of the moat in the fortification.
Curtain wall: Part of the ramparts between two bastions or angles of the fortress.
Rampart: A defensive wall or fortification generally featuring a moat.

Here are 10 facts you might not know about Polygonal fort:

1. Origin

The polygonal system of forts originated in France. Général Raymond Adolphe Séré de Rivières (1815-95) introduced France to a new era of fortifications. He advanced the idea of an 18th-century French engineer to use detached forts as a mode to expand the line of defence beyond the internal walls. These were called ‘barriers of iron’ that surrounded several old fortresses with new forts thus creating fortress rings.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet1
Typical polygonal fort_©thereaderwiki

2. Bastion-less system

Vauban introduced three bastion-systems where the limitations of the bastion-system were observed and overcome through the accumulation of bastion’s number and bulk. The bastion system turned obsolete in light of independent defence where the artillery system improved. 

The bastioned forts of the 17th and 18th centuries were designed to guard against cannon assaults but proved ineffective against rifled artillery and explosive shells. These drawbacks were eliminated utilizing assembly of external fortifications surrounded by moats built with caponiers and distancing them from internal fortifications.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet2
Tracings of defensive systems: bastion, tenail and polygonal_©http://ena.lp.edu.ua

3. Prussian manner of polygonal fortification

The German confederation as against its French counterpart came up with a new defensive system using polygonal tracing. To make the best use of terrain, these fortifications used the principle of girdle or ring fortress where the fort walls were established several hundred metres away from the original enclosure of walls.

These detached forts featured a polygonal plan with an unbroken line of ramparts and certain sections built as casemates for gun emplacements. The primary bastioned enceintes of these fortifications were retained or even rebuilt in some cases to prevent the enemy from infiltrating the fort.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet3
Early types of Prussian polygonal forts_©wikiwand

4. Fort Tigne as the first true polygonal fort

Built in the year 1793, Fort Tigne is a relatively small-scale fort built as the last major fortification work by the Order in Malta. The design of the fort was inspired by the writings of Montalembert and French lunettes. The most important design features were the absence of bastions and the artillery galleries built in the counterscarp.

The design of fort Tigne is the earliest example of the polygonal system that revolutionized and influenced the form of military architecture throughout most of the following century.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet10
Fort Tigne_©https://vassallohistory.wordpress.com

5. Casemate features

Certain sections of the ramparts were built as a bomb-proof room or a structure and are defined as casemates. The casemates in polygonal forts generally formed flanking galleries within the ramparts and had built-in cavaliers for gun emplacement. 

Apart from this, barrack accommodations and observation posts were also located in these casemates.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet4
Heavility protected casemates seen in Fort d’Uxegney_©wikipedia

6. Other salient features

Polygonal forts had a variety of features such as ablution rooms, stores, kitchens, laboratories, lavatories, medical and workshop accommodations. Access to the fort was via a curving ramp cut into the gently sloped open area followed by a rolling bridge over the ditch to reach the gatehouse.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet5
Gatehouse set deep in the scarp of Fort Madliena_©military.wikia.org

7. Placement of Armament

Polygonal forts featured a different system for the placement of armaments. The placement was done in splits with the heaviest guns mounted on the forward face while the flanks of work were defended by smaller guns. 

Both the forward and flank faces were surrounded by gently sloped open areas known as glacis. For defence and additional assistance, these forts had flanking galleries, mortar batteries and caponiers.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet6
Gun emplacements_© https://vassallohistory.wordpress.com

8. Robust style of fortification

These forts displayed advanced defence mechanisms with the improvised design of moats or ditches. The ditches became deeper, more vertical and were directly cut into the native rock. These ditches were laid out as a series of lines surrounding the fortified area and featured independent defence blockhouses (caponiers) with the firing position cut into the outer face of the ditch.

Polygonal forts sometimes also featured massive fortified barracks or defensible keep-like structures. Hence the overall form displayed a more unified and sturdy fortification system.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet7
South ditch, Fort Delimara_©military.wikia.org

9. Larger defensive scheme

The fort maintained a low profile to provide a minimum target area to the enemy lines. These forts provided vigorous and defensible gun platforms.

Polygonal forts were planned as ‘forward batteries’ to keep the enemies engaged and prevent the destruction of more vulnerable areas like dockyards and rail centers. Hence, these were built keeping in mind the larger context of the defensive scheme.

The polygonal fort is the type of fortification that originated in the late 18th century in response to the vulnerabilities of star forts. This type of fortification saw the evolution of the forts into a bastion less system. The bastion was no longer the most significant element needed to protect the curtain wall. - Sheet8
Placement of forward battery_©https://vassallohistory.wordpress.com

10. The present condition of polygonal forts

In most of the forts in Malta, externally the forts are in fair condition but showcase the eroded faces of limestone in the counterscarp and scarp areas. In certain places, it has eroded to an extent that the complete face has collapsed into the ditch. These forts do not have public internal access.

Sheet
Fort Mockton_©Hampshire Hub Partnership/ www.hants.gov.uk/

While most of the forts have not been maintained and conserved, some have been restored and developed as luxury hotels, resorts and museums.

References

Author

Surabhi is a student of architecture and is trying to figure out how she can contribute to the field and society. She finds architectural writing as an escape to a world full of possibilities and hope. Her curiosity, zest to learn, explore and share, is what keeps her going.

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