Douro is a region of Portugal which is famous for the production of Port wine.
Port is a fortified wine (one to which a spirit has been added) which has been made in the region since the late 17th Century. The fortification agent used is a grape spirit known as aguardente, usually referred to in English as 'brandy'.
The original purpose of the brandy was to prolong the life of the wine and preserve it during travelling. Traditionally, port is made with 4 parts wine to 1 part brandy.
Douro region of Portugal: