Porto is Portugal's second largest city and the capital of the Northern region, and a busy industrial and commercial centre. The city isn't very populous (about 240,000 inhabitants), but the Porto metropolitan area has some 2 million inhabitants in a 50-km radius, with cities like Vila Nova de Gaia, Vila do Conde, Póvoa de Varzim and Espinho.
The city is built at the high ground overlooking the Douro River estuary's northern side, and its historical centre was declared a WV-Unesco-icon-small.svg UNESCO World Heritage Site in 1996. It has been continuously inhabited since at least the 4th century BC.
Porto was named by the Romans Portus Calle (the origin of the entire present country's name), the city is nowadays officially styled A muito nobre, sempre leal e invicta cidade do Porto (the very noble, always loyal, and undefeated city of The Harbor). This is usually shortened to "a Cidade Invicta" (the undefeated city) a title won because of Porto's unparalleled resistance against hostile troops during the 1820s.