Carnot wall

As conceived by Carnot, they formed part of an innovative but controversial system of fortification intended to defend against artillery and infantry attack.

[7] From the late 17th century the model system of fortification was considered to be that based on the bastion trace of Vauban, Louis XIV's military engineer.

The outer side of the ditch would have a glacis, a gently outwardly sloping earth bank at a slightly lower level than the ramparts.

[13] As against this method Carnot's system did away with the covered way and steep counterscarp and made the glacis slope back into the ditch.

This had a chemin des rondes, or sentry path, to the rear allowing defenders to move along behind the wall.

As well as firing at attackers the defenders were able to make sorties from behind the wall up the countersloping glacis.

[21] Whilst the Carnot wall was extensively employed in fortifications in continental Europe there was resistance to its use in Britain, for the reasons stated above.

[22] A rampart of equal height with the wall was built in front of it to represent that of a real fort.

Their object was to test whether artillery at a distance could breach the walls by firing at high angles.

[22] Those conducting the experiments concluded that the wall could be severely damaged even if the besiegers' gunners could not see it.

In his 1849 book "An Essay on a Proposed New System of Fortification: with Hints for its Application to our National Defences", James Fergusson outlined the advantages of the Carnot wall, though without wholly endorsing its use.

[26] Fergusson also commented that the 1824 Woolwich experiments, which had influenced subsequent fort design, had given "every possible advantage in favour of the attack".

[27] He argued that, even were a breach to be made in the wall, the defenders could easily attack the besiegers, making an assault on the fort hazardous.

[27] The first fort to be built in Britain with a Carnot wall was in 1854 at the mouth of the river Arun at Littlehampton in West Sussex.

[29] Following the Royal Commission on the Defence of the United Kingdom of 1859 several forts with Carnot walls were built.

A treatise on the defence of fortified places: Written under the direction and published by command of Buonaparte, for the instruction and guidance of the officers of the French Army.

Observations on modern systems of fortification: including that proposed by M. Carnot, and a comparison of the polygonal with the bastion system; to which are added, some reflections on intrenched positions, and a tract on the naval, littoral, and internal defence of England.

An essay on a proposed new system of fortification: with hints for its application to our national defences.