Concentric castle

[1] The layout was square (at Belvoir and Beaumaris) where the terrain permitted, or an irregular polygon (at Krak and Margat) where curtain walls of a spur castle followed the contours of a hill.

[2] Historians (in particular Hugh Kennedy) have argued that the concentric defence arose as a response to advances in siege technology in the crusader states from the 12th to the 13th century.

However, the two walls facing the land are built on the same defensive principles as other crusader castles in the same period, rivalling the defences at Krak.

It has also been pointed out that the concentric layout suited the requirements of military orders such as the Hospitallers in resembling a monastery and housing a large garrison.

As Beaumaris was built on flat terrain rather than a spur, it was both necessary and possible to build walls and towers facing in all directions, giving a very regular, almost square, floor plan to the castle.

Some influence from crusader fortification has been conjectured, but the amount of technology transfer from the East and much earlier Byzantine examples remains controversial among historians.

[1] In the German-speaking states of the Holy Roman Empire, many castles had double curtain walls with a narrow ward between them, referred to as a Zwinger.