Columbia subject headings:
Catalonia (Spain)--History.
Fortification--Spain--Catalonia--History.
Military architecture--Spain--Catalonia--History.
Harvard subject headings:
Catalonia (Spain)--History.
Ebro River Valley (Spain)--History.
Fortification--Spain--Catalonia--History.
Fortification--Spain--Ebro River Valley--History.
Fortification--Spain--Tortosa--History.
Tortosa (Spain)--History.
Princeton subject headings: