Columbia subject headings:
Harvard subject headings:
Railroad tunnels--Italy, Central.
Railroad tunnels--Italy--Apennines.
Railroads--Italy, Central.
Railroads--Italy--Bologna.
Railroads--Italy--Florence.
Princeton subject headings:
Railroad tunnels--Italy, Central.
Railroad tunnels--Italy--Apennines.
Railroads--Italy, Central.
Railroads--Italy--Bologna.
Railroads--Italy--Florence.