Columbia subject headings:
Duero River (Spain and Portugal)--Antiquities, Roman--Congresses.
Duero River (Spain and Portugal)--Antiquities--Congresses.
Excavations (Archaeology)--Duero River Valley (Spain and Portugal)--Congresses.
Neolithic period--Duero River (Spain and Portugal)--Congresses.
Paleolithic period--Duero River Valley (Spain and Portugal)--Congresses.
Harvard subject headings:
Duero River (Spain and Portugal)--Antiquities, Roman--Congresses.
Duero River (Spain and Portugal)--Antiquities--Congresses.
Excavations (Archaeology)--Duero River Valley (Spain and Portugal)--Congresses.
Neolithic period--Duero River (Spain and Portugal)--Congresses.
Paleolithic period--Duero River Valley (Spain and Portugal)--Congresses.
Princeton subject headings: