I posted one of my pics of the picturesque Douro Valley yesterday. Except for the steepest parts, it's all vineyards.
The Douro Valley has produced plenty of table wines since Roman times, but is most famous for its Port Wines.
The table wine vines are irrigated, but the vines destined for Port are not.
Port Wines are a 17th Century invention, traditionally transported (mostly by Brits) from the town of Porto at the mouth of the Douro - hence Port.
I've never been much of a Port drinker, but I had a bit in Portugal. Whites and Tawnies. Nice. Unlike table wines, I can't tell much difference between expensive and cheaper Ports but connoisseurs can.
Here's a Brief History of Port Wine
Here's one of my pics of the valley, with the Douro, from the Ventozelo Hotel and Quinta.