Columbia subject headings:
Architecture, Romanesque--Conservation and restoration--Italy--Pisa--Congresses.
Bell towers--Conservation and restoration--Italy--Pisa--Congresses.
Leaning Tower (Pisa, Italy)--Congresses.
Pisa (Italy)--Buildings, structures, etc.--Congresses.
Harvard subject headings:
Leaning Tower (Pisa, Italy)--Congresses.
Pisa (Italy)--Buildings, structures, etc.--Congresses.
Towers--Conservation and restoration--Italy--Pisa--Congresses.
Princeton subject headings:
Leaning Tower (Pisa, Italy)--Congresses.
Pisa (Italy)--Buildings, structures, etc.--Congresses.
Towers--Conservation and restoration--Italy--Pisa--Congresses.