Columbia subject headings:
Fortification--Poland--Masovia.
Fortification--Poland--Podlasie (Region)
Masovia (Poland)--Antiquities.
Podlasie (Poland : Region)--Antiquities.
Poland--Antiquities.
Harvard subject headings:
Fortification--Poland--Masovia.
Fortification--Poland--Podlasie.
Masovia (Poland)--Antiquities.
Podlasie (Poland : Region)--Antiquities.
Poland--Antiquities
Princeton subject headings: