If you’re unfamiliar with stamp collectors exhibiting their collections, this may be an interesting experience. For those of us who are familiar, it’s a very nicely done philatelic exhibit on the subject of European Castles. The link follows:
From the site:
“A review of the evolution and history of European Castles, from ancient and Roman fortifications to Renaissance’s castle-palaces, and including contributions made by Byzantines, Arabs, and Crusaders, who strongly influenced the defensive military architecture of Europe.”
I recommend viewing it but make sure you’ve got at least an hour free to do it.
Archaeology Study Unit 