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.
De ydre forsvarsværker består af befæstning til artilleri, og deres nuværende udseende fik de i 1700-tallet, selvom visse dele, inklusive den østlige del af French Spur, kan dateres tilbage til Mary of Guises regeringsperiode i 1550'erne.