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.