Columbia subject headings:
London (England)--Buildings, structures, etc.
Tower of London (London, England)
Harvard subject headings:
Fortification--England--London--History.
Great Britain--History.
London (England)--Buildings, structures, etc.
London (England)--History.
Prisons--England--London--History.
Tower of London (London, England)--History.
Princeton subject headings:
London (England)--Buildings, structures, etc.
Tower of London (London, England)