Columbia subject headings:
Arch bridges--Portugal--History.
Architecture, Ancient--Portugal.
Bridges, Roman--Portugal--History.
Bridges--Portugal--Design and construction.
Portugal--Buildings, structures, etc.
Stone bridges--Portugal--History.
Harvard subject headings:
Arch bridges--Portugal--History.
Architecture, Ancient--Portugal.
Bridges, Roman--Portugal--History.
Bridges--Portugal--Design and construction.
Portugal--Buildings, structures, etc.
Stone bridges--Portugal--History.
Princeton subject headings:
Arch bridges--Portugal--History.
Architecture, Ancient--Portugal.
Bridges, Roman--Portugal--History.
Bridges--Portugal--Design and construction.
Portugal--Buildings, structures, etc.
Stone bridges--Portugal--History.