Columbia subject headings:
Harvard subject headings:
Concrete--History--Congresses.
Floors--History--Congresses.
Historic sites--Congresses.
Mortar--History--Congresses.
Princeton subject headings:
Excavations (Archaeology)--Congresses.
Floors, Concrete--History--Congresses.
Mosaic floors--History--Congresses.
Pavements--History--Congresses.