expensive, scheme. In the end a compromise was built, and was complete by 1714. The main front wall was extended outwards, to form Guardhouse Square. This had the effect of creating two defensive walls, both of which were fronted by ditches defended by covered firing galleries known as caponiers.
One of the caponiers survives and is accessible from Guardhouse Square by a narrow staircase.
To the rear of the walls, chambers called casemates were built to strengthen the wall, and to provide gun emplacements. The French Spur was modified slightly to allow more cannons to be mounted. The buildings within Guardhouse Square date from the 19th century.
The Outer Defences comprise artillery fortifications, and were built in their present form in the 18th century, although some parts, including the French Spur at the east end, date back to the regency of Mary of Guise in the 1550s. The French Spur was originally an ear-shaped bastion known as an orillon, and contained gun emplacements which protected the main spur.
This projecting spur was fronted by an earth ramp called a talus, and was entered via a drawbridge over a ditch. Excavations in the 1970s showed that much of the original stonework remains within the 18th-century defences.
Following the attempted Jacobite invasion of 1708, improvements to the castle's defences were ordered as a matter of priority. A scheme of new defences was proposed by Theodore Dury, although this was criticised by one Captain Obryan, who put forward his own, much more