Polygonal fort

A polygonal fort is a fortification in the style that appeared in the end of the eighteenth century and evolved around the middle of the nineteenth century, in response to the development of powerful explosive shells.

The complex and sophisticated designs of star forts that preceded them were highly effective against cannon assault, but proved much less effective against the more accurate fire of rifled guns and the destructive power of explosive shells. The polygonal style of fortification is also described as a "flankless fort". Their low profile makes them easy to overlook.

One of the earliest polygonal forts in the world is Fort Tigné on Tigné Point, Malta, which was built by the Order of Saint John between 1792 and 1795. After the British took Malta in 1800, they considered this fort as the "perfection of a small fort without flanks ... capable of considerable resistance", and the British built a battery on Anholt (1812) and a fort on Vido (1824) in a similar design. The British went on to build several other polygonal forts and batteries on Malta from 1872 to 1909, the first one being Fort St. Rocco.

Many were also built in the United Kingdom during the government of Lord Palmerston, and so they are also often referred to as Palmerston forts.

In response to the vulnerabilities of star forts, military engineers evolved a much simpler but more robust style of fortification.

The ditch became deep and vertical sided, cut directly into the native rock. It was laid out as a series of straight lines surrounding the fortified area that gives this style of fortification its name.

The ditch was swept by fire from defensive blockhouses (caponiers) set in the ditch, and firing positions cut into the outer face of the ditch itself (counterscarp battery).

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