Columbia subject headings:
Charles V, Holy Roman Emperor, 1500-1558.
Fortification--Spain--History--16th century.
Siege warfare--Spain--History--16th century.
Spain--History--Charles I, 1516-1556.
Harvard subject headings:
Fortification--Europe--History--16th century.
Fortification--Spain--History--16th century.
Spain--Colonies--Defenses.
Princeton subject headings:
Fortification--Europe--History--16th century.
Fortification--Spain--History--16th century.
Spain--Colonies--Defenses.