Columbia subject headings:
Harvard subject headings:
Ecology--Europe--History--Congresses.
Europe--Antiquities, Roman--Congresses.
Europe--Economic conditions--Congresses.
Europe--History--476-1492--Congresses.
Rome--History--Empire, 30 B.C.-284 A.D.--Congresses.
Princeton subject headings:
Ecology--Europe--History--Congresses.
Europe--Antiquities, Roman--Congresses.
Europe--Economic conditions--Congresses.
Europe--History--476-1492--Congresses.
Rome--History--Empire, 30 B.C.-284 A.D.--Congresses.