page_title: Polygonal fort
section_title: Theories of Montalembert and Carnot
hierarchical_section_title: Polygonal fort / Theories of Montalembert and Carnot
caption_attribution_description: Français&#160;: Entrée du Fort de Querqueville
context_page_description: A polygonal fort is a type of fortification originating in France in the late 18th century and fully developed in Germany in the first half of the 19th century. Unlike earlier forts, polygonal forts had no bastions, which had proved to be vulnerable. As part of ring fortresses, polygonal forts were generally arranged in a ring around the place they were intended to protect, so that each fort could support its neighbours. The concept of the polygonal fort proved to be adaptable to improvements in the artillery which might be used against them, and they continued to be built and rebuilt well into the 20th century.
context_section_description: Marc René, marquis de Montalembert (1714–1800) envisaged a system to prevent an opponent from establishing their parallel entrenchments by an overwhelming artillery barrage from a large number of guns, which were to be protected from return fire. The elements of his system were the replacement of bastions with tenailles, resulting in a defensive line with a zigzag plan, allowing for the maximum number of guns to be brought to bear and the provision of gun towers or redoubts (small forts), forward of the main line, each mounting a powerful artillery battery. All the guns were to be mounted in multi-storey masonry casemates, vaulted chambers built into the ramparts of the forts. Defence of the ditches was to be by caponiers, covered galleries projecting into the ditch with numerous loopholes for small arms, compensating for the loss of the bastions with their flanking fire. Montalembert argued that the three elements, would provide long-range offensive fire from the casemated main curtain, defence in depth from the detached forts or towers and close-in defence from the caponiers. Montalembert described his theories in an eleven-volume work called La Fortification Perpendiculaire which was published in Paris between 1776 and 1778. He summarised the benefits of his system thus; "...all is exposed to the fire of the besieged, which is everywhere superior to that of the besieger, and the latter cannot advance a step without being hit from all sides".
  A full realisation of Montalembert's ambitious plans for a great inland fortress was never attempted. Almost immediately after publication, unofficial translations into German were being made of Montalembert's work and were being circulated amongst the officers of the Prussian Army. In 1780, Gerhard von Scharnhorst, a Hanoverian officer who went on to reform the Prussian Army, wrote that "All foreign experts in military and engineering affairs hail Montalembert's work as the most intelligent and distinguished achievement in fortification over the last hundred years. Things are very different in France". The conservative French military establishment was wedded to the principles laid down by Vauban and improvements made by his later followers, Louis de Cormontaigne and Charles Louis de Fourcroy. What little political influence the aristocratic Montalembert had during the Ancien Régime was lost following the French Revolution in 1792.
  Despite the conservatism of the French engineer corps, two French engineers experimented on a modest scale with Montalembert's ideas for detached forts. Jean Le Michaud d'Arçon, ironically one of Montalembert's detractors, designed and built a number of lunettes (an outwork resembling a detached bastion) which were in accord with Montalembert's concepts. These lunettes were constructed at Mont-Dauphin, Besançon, Perpignan and other border fortresses, commencing in 1791 shortly before the Revolution. In the same year, Antoine Étienne de Tousard took up a position on Malta as an engineer to the Order of Saint John and was instructed to design a small fort to command the entrance to Marsamxett Harbour called Fort Tigné. Exactly how Tousard became acquainted with d'Arcon's lunette design is unknown, but the resemblance is too close to be coincidental. It was, like d'Arcon's works, quadrilateral in plan, divided by a traverse with a circular tower keep in the rear and the surrounding ditch was protected by counterscarp galleries. Fort Tigné, however, was a fully defensible and self-contained fort, larger and more sophisticated than d'Arcon's outworks, and is regarded as being the first true polygonal fort.  
  Montalembert's work was also allowed to take concrete form during his lifetime in the field of coastal fortification. In 1778, he was commissioned to build a fort on the Île-d'Aix, defending the port of Rochefort, Charente-Maritime. The outbreak of the Anglo-French War forced him hastily to build his casemated fort from wood but he was able to prove that his well-designed casemates were capable of operating without choking the gunners with smoke, one of
caption: Fort de Querqueville, one of the casemated coastal forts at Cherbourg, which was based on Montalembert's system.
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