Columbia subject headings:
Bajo Guadalquivir Canal (Spain)
Forced labor--Spain--History--20th century.
Political persecution--Spain--History--20th century.
Political prisoners--Spain--History--20th century.
Spain--History--Civil War, 1936-1939--Conscript labor.
Harvard subject headings:
Bajo Guadalquivir Canal (Spain)
Canals--Spain--Andalusia--Design and construction--History--20th century.
Convict labor--Spain--Andalusia--20th century.
Forced labor--Spain--Andalusia--History--20th century.
Forced labor--Spain--History--20th century.
Political persecution--Spain--History--20th century.
Political prisoners--Spain--Andalusia--History--20th century.
Political prisoners--Spain--History--20th century.
Spain--History--Civil War, 1936-1939--Conscript labor.
Princeton subject headings: