Founded as a Roman city, Barcelona became the capital of the County of Barcelona. After merging with the Kingdom of Aragon, Barcelona continued to be an important city in the Crown of Aragon. Besieged several times during its history, Barcelona has a rich cultural heritage and is today an important cultural centre and a major tourist destination. Particularly renowned are the architectural works of Antoni Gaudí and Lluís Domčnech i Montaner, which have been designated UNESCO World Heritage Sites. The headquarters of the Union for the Mediterranean is located in Barcelona. The city is known for hosting the 1992 Summer Olympics as well as world-class conferences and expositions and also many international sport tournaments.
Barcelona is today one of the world's leading tourist, economic, trade fair/exhibitions and cultural-sports centres, and its influence in commerce, education, entertainment, media, fashion, science, and the arts all contribute to its status as one of the world's major global cities. It is a major cultural and economic centre in southwestern Europe (Iberian Peninsula), 24th in the world (after Zürich, before Frankfurt) and a financial centre (Diagonal Mar and Gran Via). In 2008 it was the fourth most economically powerful city by GDP in the European Union and 35th in the world with GDP amounting to €177 billion. In 2012 Barcelona had a GDP of $171.0 billion; it is lagging Spain on both employment and GDP per capita change. In 2009 the city was ranked Europe's third and one of the world's most successful as a city brand. In the same year the city was ranked Europe's fourth best city for business and fastest improving European city, with growth improved by 17% per year, but it has since been in a full recession with declines in both employment and GDP per capita, with some recent signs of the beginning of an economic recovery. Barcelona is a transport hub with one of Europe's principal seaports, an international airport which handles above 35 million passengers per year, an extensive motorway network and a high-speed rail line with a planned link to France and the rest of Europe.