Port is a fortified, typically red and sweet, wine that comes in a number of styles. It is produced in a demarcated region in the Douro Valley in northern Portugal, inland from the eponymous city of Porto.

Non-fortified wine has been made in the Douro Valley since Roman times, and became an important export following the establishment of the Kingdom of Portugal in 1143. The 1386 Treaty of Windsor established close trading and diplomatic links between England and Portugal, with many English merchants settling in Portugal and exporting wines back to England from Viana do Castelo on the broad estuary of the Lima River. These light and astringent wines came from the nearby Minho region, and compared poorly to the more expensive wines of Bordeaux.

In 1667, Colbert, first minister to Louis XIV, restricted the import of English goods into France, provoking Charles II to prohibit the import of French wines. The English merchants at Viana do Castelo stepped in to fill the supply gap. To satisfy English tastes, they began sourcing more robust, full-bodied wines from the then remote upper Douro Valley. These wines could not be transported over land to Viana do Castelo, compelling the merchants to relocate a few miles south to Oporto near the mouth of the Douro River.

The trade in the wines of Oporto or ‘port wines’ received a further fillip from the Methuen Treaty of 1703, which led, amongst others, to a fall in the duty on Portuguese wines exported to England. Port wines soon became a victim of their own success, with some producers and shippers adding sugar or elderberry in a bid to improve their often thin, overstretched offerings. In 1756 (just one year after the catastrophic Lisbon earthquake) these problems together with a resulting fall in demand impelled the then prime minister of Portugal the Marquês de Pombal to regulate production. This led to the demarcation of the Douro vineyard area by 335 stone pillars or marcos pombalinos, and, in the following year, to the classification of the vineyards according to quality.

Shippers sometimes added a small amount of brandy or grape spirit to stabilize the wine on its voyage to England. Over time, it became common practice to add the brandy before the wine had finished fermenting since this resulted in a fresher, sweeter, and more appealing wine. And it soon became apparent that these fortified wines also had a vastly superior ageing potential. As bottles became progressively more elongated in shape, it became possible to store them on their side and thus to cellar single vintage wines. 1820 produced such an exceptional vintage that subsequent vintages had to be fortified to even hold comparison, and by 1850 the practice of fortification had become near universal.

During the occupation of Oporto by Napoleon’s army from 1809 to 1811 the port trade came to virtual standstill. Trading also suffered in the 1820s and early 1830s from political turmoil culminating in the Portuguese Civil War over the royal succession and the 1832 siege of Oporto. Having withstood these early setbacks, the port trade flourished in the latter part of the 19th century, and it is in this period that it became customary to ‘declare’ the finest vintages. These Halcyon days came to an abrupt end in 1868 with the arrival of the Phylloxera louse from North America via the Southern Rhone, which resulted in such severe damage as to ruin several long established producers. The port trade did not fully recover until the 1890s, by which time the majority of vines had been grafted onto Phylloxera-resistant American rootstock.

Until well into the 20th century, port was carried downriver to the cellars of Vila Nova de Gaia (just across the river from Porto) on flat-bottomed vessels called barcos rabelos. So as to best navigate through treacherous rapids, the barcos rabelos were equipped with a long steering oar operated from the top of a raised platform. A broad sail enabled them to make the return journey upriver, although in certain parts they required further assistance from oxen straining on a towpath. Until the end of the 18th century, a waterfall in a narrow gorge had obstructed passage into the remote Upper Douro (Douro Superior). The opening of this gorge to river traffic in the 1780s greatly facilitated the emergence of some of today’s finest Douro estates. The Duoro of today has been dammed and is comparatively easy to navigate, but port is sent to the sea by road and rail rather than by the river. The last commercial voyage of a barco rabelo took place in about 1961.