Founded as a Roman city, in the Middle Ages Barcelona became the capital of the County of Barcelona. After joining with the Kingdom of Aragon to form the confederation of the Crown of Aragon, Barcelona, which continued to be the capital of the Principality of Catalonia, became the most important city in the Crown of Aragon and the main economic and administrative centre of the Crown, only to be overtaken by Valencia, wrested from Arab domination by the Catalans, shortly before the dynastic union between the Crown of Castile and the Crown of Aragon in 1492. 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 Domènech i Montaner, which have been designated UNESCO World Heritage Sites. Since 1450, it is home to the University of Barcelona, widely considered the most prestigious university in Spain. The headquarters of the Union for the Mediterranean are 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.