The Douro's role in shaping Porto's commercial identity began in 1756, when the Marquês de Pombal demarcated the world's first protected wine region along its upper reaches. For two centuries, rabelo boats—flat-bottomed oak vessels with square sails—ferried port wine barrels 120 kilometres downstream from the Pinhão valley to Vila Nova de Gaia's riverside lodges. By the 1960s, road transport had rendered the rabelos obsolete, yet their silhouette remains the Douro's defining visual motif. Today, Porto Douro River boat cruise with port wine tasting experiences depart from Cais da Ribeira, the medieval quayside where cargo once transferred from river to Atlantic trade routes. The Six Bridges itinerary passes beneath Dom Luís I Bridge, an 1886 wrought-iron arch designed by Théophile Seyrig, Gustave Eiffel's former partner. The double-deck structure connects Porto's Ribeira district to the port lodges of Gaia, its upper span rising 45 metres above the waterline. Downstream, the Arrábida Bridge's 270-metre concrete arch held the world record for its type between 1963 and 1977. Each crossing offers a study in engineering ambition: from 19th-century riveted iron to mid-century prestressed concrete. Port wine cellars occupy the south bank opposite Ribeira—Taylor's, Sandeman, Ferreira—where ruby, tawny, and vintage expressions age in oak casks beneath vaulted stone ceilings. The fortified wine tradition arose from necessity: adding grape spirit halted fermentation, preserving sweetness and ensuring the wine survived the voyage to England. Douro Valley tours extend this narrative upriver, where UNESCO-protected terraces climb schist slopes at gradients exceeding 30 degrees. Quinta estates offer tastings of single-vineyard ports alongside the ungrafted vines that produce them, many pre-dating the phylloxera epidemic. A Douro river tour from Porto bridges the gap between urban embarkation and agricultural hinterland, tracing the route that transformed regional harvest into global commodity.