Columbia subject headings:
Architecture--Italy--Romagna.
Castles--Italy--Romagna.
Pio family--Homes and haunts.
Towers--Italy--Romagna.
Harvard subject headings:
Architecture--Italy--Romagna.
Castles--Italy--Romagna.
Pio family.
Towers--Italy--Romagna.
Princeton subject headings:
Architecture--Italy--Romagna.
Castles--Italy--Romagna.
Pio family--Homes and haunts.
Towers--Italy--Romagna.