Mountains are the ideal place to build a castle, as the difficult access provides security while the elevation offers a good overview of the surrounding terrain. But where to place your defensive fortress if you are in the Netherlands, where most of the land is below sea level?
In the case of the Burcht van Leiden (Castle of Leiden), a shell keep built in the 11th century, the fortress sits on top of a 30-foot motte, or artificial hill, which was built up on a fork of the Rhine River. For about two centuries this fortress was the main defensive structure of the city and home to the burggraaf (viscount). Its thick tuff and brick walls rise about 20 feet high, making this citadel a particularly squat example of a European medieval castle.
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