Columbia subject headings:
Harvard subject headings:
Harbors--Italy--History--Congresses.
Harbors--Spain--History--Congresses.
Italy--Commerce--History--Congresses.
Shipping--Italy--History--Congresses.
Shipping--Spain--History--Congresses.
Spain--Commerce--History--Congresses.
Princeton subject headings:
Italy--Commerce--Congresses.
Italy--History, Naval--Congresses.
Spain--History, Naval--Congresses.