A spur castle is a type of medieval fortification that uses its location as a defensive feature. The name refers to the location on a spur projecting from a hill. Ideally, a spur castle would be defended on three sides by steep hillsides, with the only vulnerable side the one where the spur joins the next hill. Depending on the local topography, a spur castle may depend mostly on its inaccessible location, or combine it with defensive features such as walls and towers. A typical feature is a neck ditchcutting off the spur from the rest of the hill. When the spur is long and narrow, the term ridge castle is sometimes used as well. A long spur castle is sometimes, but not always, subdivided into a lower ward and a more strongly defended upper ward. Spur and hilltop castles were introduced by the Franks in order to hinder the deployment of the increasing use of the counterweight trebuchet. In the case of spur castles, heavy siege machinery could only be deployed on the uphill side enabling defensive works and forces to be concentrated there.
In the castle at Saône, the defences are concentrated on the vulnerable side of the spur, most notably a deep ditch. The lower bailey at Saône has weaker walls and towers.
The Teutonic Knights' Montfort Castle is a narrow ridge castle that relies for its defence on the steep rocky hillsides, lacking many of the innovations of the larger crusader castles and resembling smaller German baronial castles.
The Alamut Castle in Persia was positioned atop a narrow rock base approximately 180 m above ground level. It was thought to be impregnable to direct attack.
The Alcázar of Segovia in Spain is located on a narrow spur with deep drops all around except from the east where it is approached on level ground.
Stirling Castle in Scotland is located on a narrow spur with drops on three sides and a gentle slope providing access from the south-east.
