Barcelona is the capital, 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. It is the 11th-most populous municipality in the European Union and sixth-most populous urban area in the European Union after Paris, London, Rhine-Ruhr Area, Madrid and Milan with the population 4,185,000. 4.9 million people live in Barcelona metropolitan area. The main part of a union of adjacent cities and municipalities named Área Metropolitana de Barcelona (AMB) with a population of 3,186,461 in area of 636 km² (density 5.010 hab/km²).
It is located on the Mediterranean coast (41°23′N 2°11′E / 41.383°N 2.183°E / 41.383; 2.183) 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 recognised as a global city because of its importance in finance, commerce, media, entertainment, arts and international trade. 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 the Madrid-Barajas Airport (handles about 30 million passengers per year). 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. ( source Wikipedia )