Columbia subject headings:
Duomo di Siena--Congresses.
Pavements, Mosaic--Italy--Siena--Congresses.
Harvard subject headings:
Duomo di Siena--Congresses.
Pavements, Mosaic--Italy--Siena--Congresses.
Princeton subject headings:
Duomo di Siena--Congresses.
Pavements, Mosaic--Italy--Siena--Congresses.