Columbia subject headings:
Fortification--Spain--Santo Domingo de la Calzada--History.
Santo Domingo de la Calzada (Spain)--Buildings, structures, etc.
Santo Domingo de la Calzada (Spain)--History, Military.
Harvard subject headings:
Fortification--Spain--Santo Domingo de la Calzada--History.
Santo Domingo de la Calzada (Spain)--Buildings, structures, etc.
Santo Domingo de la Calzada (Spain)--History, Military.
Princeton subject headings: