Columbia subject headings:
Harvard subject headings:
Architecture, Domestic--Italy--Siena--Congresses.
Architecture, Domestic--Italy--Tuscany--Congresses.
Arts, Italian--Italy--Tuscany--Congresses.
Siena (Italy : Province)--Buildings, structures, etc.--Congresses.
Siena (Italy)--Buildings, structures, etc.--Congresses.
Princeton subject headings:
Architecture, Domestic--Italy--Siena--Congresses.