An important Atlantic harbor since Roman times, by the end of the fifteenth century, Porto, at the mouth of the river Douro, was a well-established port with a mercantile bourgeoisie strong enough to craft a role for itself independent of both the church and the court. Over the following century, the city developed its trading potential by, among other things, recruiting pilots to navigate the river's treacherous bar, building lighthouses, and curbing Atlantic pirates. Thus in the seventeenth century, Porto increasingly controlled northern Portugal's growing trade with Brazil and northern Europe. Early prevalence of sugar, cereals, and sumac in cargoes gave way in the late 1600s to textiles and wines. Porto had exported wine since medieval times, but trade expanded as European wars drove French wines from several northern European markets, in particular those in England, where a taste for wines of the Douro (which soon became known as "port") developed. Though it guaranteed lower duties on Portuguese wine than on French, the famous Methuen commercial treaty of 1703 had less effect on wine exports, which were well established, than on textile imports. Removing import protections that had sheltered them, the treaty effectively destroyed Portugal's textile industries. Merchants from the British Isles (unlike Portuguese counterparts) remained well protected, however, from the depredations of the Inquisition and, establishing a factory in the city, brought textiles and other manufactured goods from England to Porto (and Vila Nova de Gaia on the other bank of the estuary) and returned with port and other agricultural products. Wine and foreign wine traders (including merchants from the Low Countries and the Baltic) came to dominate Porto's exports. The creation in 1756 of a Portuguese quasi-monopoly to regulate wine production checked the dominance of foreigners but increased that of wine. This regulatory company itself became a major wine exporter, controlling wine trade to Brazil and discomfiting wine merchants in England.
By the end of the eighteenth century, when it reached its apogee, wine trading had significantly enriched the city of Porto as well as the major growers of the Douro Valley; consequently, its troubles in the nineteenth century impoverished both. Napoleon Bonaparte's Continental blockade disrupted trade to England from 1806 to 1810. French invasion (1807) drove the Portuguese court to Rio de Janeiro and thereby ended Portugal's ability to control trade to Brazil, which in 1822 became independent. It may have been Anglo-French peace, not war, that was most damaging, however, for across the century, Porto's grip on the English market slipped under pressure from first Spanish and then French wines. Civil war, a siege of Porto (1833–1834), and the disestablishment under the victorious liberal government of the regulatory company, further disrupted the wine trade, as did the vine diseases oïdium and phylloxera in the second half of the century. Each exposed quite painfully the city's heavy dependence on wine, though this was eased by the development of an industrial sector producing clothes and shoes and gradual export diversification towards the end of the nineteenth century.
The same period, however, saw Porto's demise as a major port with the opening (in 1895) of a new harbor at Leixôes on the coast above the estuary and beyond the treacherous bar. Since the twentieth century Leixôes has dominated the region's trade, turning Porto into a harbor for pleasure craft. Leixôes's contribution to overall Portuguese trade has nonetheless been limited by, on the one hand, the surprising rise during the twentieth century of France as the largest market for port, and on the other, increasing trade with Spain and Germany, now Portugal's major trading partners, for all three countries are primarily served by overland transport.
Fisher, H. E. S. The Portugal Trade: A Study of Anglo-Portuguese Commerce, 1700–1770. London: Methuen, 1971.
Lains, Pedro. A Economia Portuguesa no Século XIX: Crescimento, Económico e Comércio Externo, 1851–1913. Lisbon: Imprensa Nacional Casa de Moeda, 1995.
Oliveira Ramos, Luís A. de, ed. História do Porto. Porto: Porto Editora, 1994.
Silva Lopes, José. "A Economia Portuguesa no Século XX." Panorama da Cultura Portuguesa no Século XX, vol. 1, ed. Fernando Pernes. Porto: Afrontimento.