Lisbon is the capital and the largest city of Portugal, with an estimated population of 505,526 within its administrative limits in an area of 100.05 km2. Its urban area extends beyond the city's administrative limits with a population of around 2.8 million people, being the 11th-most populous urban area in the European Union. About 3 million people live in the Lisbon Metropolitan Area (which represents approximately 27% of the country's population). It is mainland Europe's westernmost capital city and the only one along the Atlantic coast. Lisbon lies in the western Iberian Peninsula on the Atlantic Ocean and the River Tagus. The westernmost areas of its metro area form the westernmost point of Continental Europe, which is known as Cabo da Roca, located in the Sintra Mountains.
Lisbon is recognised as an alpha-level global city by the Globalization and World Cities (GaWC) Study Group because of its importance in finance, commerce, media, entertainment, arts, international trade, education and tourism. Lisbon is the only Portuguese city besides Porto to be recognised as a global city. It is one of the major economic centres on the continent, with a growing financial sector and one of the largest container ports on Europe's Atlantic coast. Additionally, Humberto Delgado Airport served 26.7 million passengers in 2017, being the busiest airport in Portugal, the 3rd busiest in the Iberian Peninsula and the 20th busiest in Europe, and the motorway network and the high-speed rail system of Alfa Pendular links the main cities of Portugal (such as Braga, Porto and Coimbra) to Lisbon. The city is the 9th-most-visited city in Southern Europe, after Rome, Istanbul, Barcelona, Milan, Venice, Madrid, Florence and Athens, with 3,320,300 tourists in 2017. The Lisbon regioncontributes with a higher GDP PPP per capita than any other region in Portugal. Its GDP amounts to 96.3 billion USD and thus $32,434 per capita. The city occupies the 40th place of highest gross earnings in the world. Most of the headquarters of multinational corporations in Portugal are located in the Lisbon area. It is also the political centre of the country, as its seat of Government and residence of the Head of State.
Lisbon is one of the oldest cities in the world, and one of the oldest in Western Europe, predating other modern European capitals such as London, Paris, and Rome by centuries. Julius Caesar made it a municipium called Felicitas Julia, adding to the name Olissipo. Ruled by a series of Germanic tribes from the 5th century, it was captured by the Moors in the 8th century. In 1147, the Crusaders under Afonso Henriques reconquered the city and since then it has been a major political, economic and cultural centre of Portugal. Unlike most capital cities, Lisbon's status as the capital of Portugal has never been granted or confirmed officially – by statute or in written form. Its position as the capital has formed through constitutional convention, making its position as de facto capital a part of the Constitution of Portugal.
Lisbon has a Mediterranean climate with mild, rainy winters and warm to hot, dry summers. The average annual temperature is 17.4 °C (63.3 °F), 21.3 °C (70.3 °F) during the day and 13.5 °C (56.3 °F) at night.
In the coldest month – January – the highest temperature during the day typically ranges from 10 to 18 °C (50 to 64 °F), the lowest temperature at night ranges from 3 to 13 °C (37 to 55 °F) and the average sea temperature is 15 °C (59 °F). In the warmest month – August – the highest temperature during the day typically ranges from 25 to 32 °C (77 to 90 °F), the lowest temperature at night ranges from 14 to 20 °C (57 to 68 °F) and the average sea temperature is 20 °C (68 °F).
Among European cities with a population above 500,000, Lisbon ranks with one of the warmest winters (less than Valencia or Málaga) and one of the mildest night time temperatures, from an average of 8.3 °C (46.9 °F) in the coldest month, and 18.6 °C (65.5 °F) in the warmest month. The minimum temperature recorded in Lisbon was −1.2 °C (30 °F) in February 1956 and −1 °C (30 °F) in January 1985. The maximum temperature recorded in Lisbon was 42 °C (108 °F) on 1 August 2003.
Sunshine hours are 2,806 per year, from an average of 4.6 hours of sunshine duration per day in December to an average of 11.4 hours of sunshine duration per day in July. The annual average rainfall is 774 mm (30.5 in), being November the wettest month.