Porto or Oporto is the second-largest city in Portugal and one of the Iberian Peninsula's major urban areas. Porto city is small compared to its metropolitan area, with a population of 237,559 people. Porto's metropolitan area has an estimated 1.7 million people in an area of 2,395 km², making it the second-largest urban area in Portugal. It is recognized as a global city with a Gamma + rating from the Globalization and World Cities Research Network.
Located along the Douro River estuary in northern Portugal, Porto is one of the oldest European centres, and its core was proclaimed a World Heritage Site by UNESCO in 1996, as "Historic Centre of Porto, Luiz I Bridge and Monastery of Serra do Pilar". The historic area is also a National Monument of Portugal. The western part of its urban area extends to the coastline of the Atlantic Ocean. Its settlement dates back many centuries, when it was an outpost of the Roman Empire. Its combined Celtic-Latin name, Portus Cale, has been referred to as the origin of the name Portugal, based on transliteration and oral evolution from Latin.