The Douro river flows through the territories of Spain and Portugal. The famous Portuguese wine-region of Alto Douro with the centuries-old tradition of viticulture lies on its banks. The vineyards are situated on steep slopes that are interspersed here and there with olive and orange trees. In the valley of the river wine producers collect grapes from which port wine is made. Formerly, the wine in barrels produced in the region of Alto Douro was transported to major cities by the river.