Authentic port comes only from the Douro River Valley, located in northeast Portugal, where the hot, dry climate is ideal for growing port grapes. Wine has been produced in here since Roman times. The region was originally demarcated in 1756, predating the Bordeaux classification by nearly 100 years. It has changed little since then, comprising a total of just 800,000 acres, about one tenth planted to vineyards.

Port takes its origins from the 17th Century trade wars between the English and the French, when the imports of French wines were first prohibited, then prohibitively taxed. English wine merchants looked to Portugal for an alternative wine source. Shippers began to add brandy to the wines to stabilize them for shipping. Eventually, around 1700, wine producers began adding the brandy during fermentation rather than after to produce the sweet, higher-alcohol red wine that port has become today.

The delimitated area starts about 60 miles east of Oporto. Here, in the granite mountains, are deposits of schist, the laminated rock that forms the soil in which port grapes grow. The Douro is divided into three regions: the Baixo Corgo (bay-shoo corg-oh), the Cima Corgo (see-ma corg-oh) and the Douro Superior. Baixo Corgo (literally "below the Corgo River") is the wettest and coolest of the three and is well suited to growing grapes for young tawny and ruby ports. The warmer, more arid Cima (middle) Corgo, with its terraced, steeply sloping hillsides, produces wines destined for old tawny, single quinta and vintage ports. Further east, the Douro Superior is the hottest and driest of all.

For centuries, the rolling hills of the Baixo (or lower) Corgo produced most of the wine and still have about 50% of the total vineyard area for port. However, with the rapid growth of the English port trade in the 18th Century, producers sought new vineyard lands and moved inland to the Cima Corgo and Douro Superior.

The steep, rugged hillsides of the Douro Superior were found to produce the best wines, and it is here that Cockburn’s established its vineyard holdings. Fine quintas dot the river, including Cockburn’s Quinta dos Canais and Quinta do Tua. Cockburn’s has also pioneered viticulture on the flatter ground away from the river for high quality grapes for Special Reserve. This land is more easily farmed and is suitable for tractors. Presently, Cockburn’s is the only port house to make a sizeable investment in this area.

The climate of the Douro is one of extremes. Winters bring severe frosts while summers are long, hot and dry. Spring and autumn, however, are milder and bring the weather conditions ideal for growing the best port varietals. The 4600-foot Serra do Mãrao (serra doo mar-OW) mountains form a barrier to the Atlantic and its influence. The average rainfall of 47" at the coast rises to 59" in the mountains, then drops off dramatically to 35" at Régua, 27" at Pinhão, all the way down to 16" near the Spanish border. Summer temperatures rise steadily as one travels east, often exceeding 95¼ F.

The vines grow in a topsoil derived from a laminated rock called schist, that occasionally needs to be shattered with dynamite before planting can begin. The soil is rich in minerals and retains the scant rainfall well. Terrace design in the vineyards helps to channel and trap water while minimizing erosion.

Terraced vineyards are planted on the steeper hillsides in the Douro. Older vineyards were planted on very narrow hand-built terraces supported by stone walls, often bearing but one row of vines. More modern vineyards are planted on wider terraces, called patamares, which are bulldozed out of the hillside to accommodate two or more rows of vines and allow a small degree of mechanization. Elevation also plays an important role. Port vineyards must be below 1640 feet, as higher elevations are more subject to the cooler Atlantic climate.