Despite the common period in which castles rose to prominence in Europe, their form and design varied from region to region. In the early 11th century, the motte and keep – an artificial mound surmounted by a palisade and tower – was the most common form of castle in Europe, everywhere except Scandinavia. While Britain, France, and Italy shared a tradition of timber construction that was continued in castle architecture, Spain more commonly used stone or mud-brick as the main building material.