Medieval Castles were meant to serve the role of being a military fortification. As a result, castles were carefully designed and planned to ensure maximum strength of the structure and numerous defences were added to the castle structure to make it as impenetrable as possible.
One of the vital considerations when constructing a castle was its location. Castle builders would usually choose a strategic site that would double as an additional natural layer of protection against outside attackers. A castle built in such a strategic manner, such as one located atop a mound or outcrop, was more secure than a castle which was located on ground level.
Many medieval castles, such as those commissioned by Norman King William following his Conquest of England, were built near rivers. This was an excellent strategic location for building castles because a river provided a natural defence for the castle. As a result, the defenders didn’t have to worry for a ground assault from the riverside.
Another vital advantage of building a castle near a river was the ready availability of a large amount of water. This could be used to build a dam, augment defences such as a moats and used as a means of escape in case the castle succumbed to an attack.
In some cases, the castle was built near a river crossing so that it commanded a view of everyone who crossed the river thereby controlling the passage. Castles located near major rivers would also control the traffic which used the river as a trade route.
Normans were successful in most of their conquests thanks to the motte-and-bailey castles they used. Such castles typically had their keeps located over steep mounds of earth. This later became impractical as castles came to be built in stone.
However, locating a stone castle over a rock outcrop became one of the best ways of benefiting both from stone construction as well as the advantage of being at a height. A castle located thus had a vital advantage of elevation against any outside attackers, giving the castle defenders ample opportunity to fight back effectively. It was also hard for the attackers to scale such a castle and reach its walls.
Many medieval castles, especially those located in Western Europe and the Iberian Peninsula, were located on key points at mountain passes. This gave the castle a critical strategic advantage due to their location. Such castles would command unchecked control of the pass and decided who should be allowed to cross the pass. In the case of an attack, such a strategically located castle could take on an enemy many times the size of its own garrison and still remain undefeated.
Apart from choosing geographical settings to enhance the location and advantage of a castle, trading and travelling routes were also a significant point of consideration when choosing a castle’s location. A castle constructed near a major crossroad essentially had control of the choke-point of the crossroad and could gather taxes from the travellers, keep an eye on the traffic and be stationed on a popular route of commerce. Such advantages often led to the construction of castles on major crossroads.