Barcelona, is the capital and most populous city of the Autonomous Community of Catalonia and the second largest city in Spain, with a population of 1,615,908 in 2008, while the population of the Metropolitan Area was 3,161,081. It is the central nucleus of the Urban Region of Barcelona, which relies on a population of about 5.5 million. It is located on the Mediterranean coast between the mouths of the rivers Llobregat and Besòs and is bounded to the west by the Serra de Collserola ridge (512 m/1,680 ft). Barcelona is a major economic centre with one of Europe's principal Mediterranean ports, and Barcelona International Airport is the second largest in Spain after Madrid-Barajas Airport. Founded as a Roman city, Barcelona became the capital of the Counts of Barcelona. After merging with the Kingdom of Aragon, it became one of the most important cities of the Crown of Aragon. Besieged several times during its history, Barcelona is today an important cultural centre and a major tourist destination and has a rich cultural heritage. Particularly renowned are architectural works of Antoni Gaudí and Lluís Domènech i Montaner that have been designated UNESCO World Heritage Sites. The city is well known in recent times for the 1992 Summer Olympics. The headquarters of the Union for the Mediterranean are located in Barcelona. As the capital of Catalonia, Barcelona houses the seat of the Catalan government, known as the Generalitat de Catalunya; of particular note are the executive branch, the parliament, and the Supreme Court of Catalonia. The city is also the capital of the county (comarca) of the Barcelonès.