Columbia subject headings:
Fortification--Poland.
Fortification.
Polish people.
Vistula River Valley (Poland)--Antiquities.
Harvard subject headings:
Fortification
Fortification--Poland
Polish people
Vistula River Valley (Poland)--Antiquities.
Princeton subject headings:
Fortification--Poland.
Polish people.
Vistula River Valley (Poland)--Antiquities.