With over one million inhabitants, Cologne is the most populous city in North Rhine-Westphalia; after Berlin, Hamburg and Munich the fourth largest city of Germany. The city is considered as the metropolitan center of Rhein-Ruhr region with about ten million inhabitants. Cologne was founded in Roman times under the name Oppidum Ubiorum, and in 50 AD as Colonia Claudia Ara Agrippinensium raised to a city. The city has an international significance as an economic and cultural metropolis. It is a carnival center and seat of many associations and media companies and is considered to be one of the leading locations of the worldwide art trade. In addition, Cologne is one of the most important tourist destinations in Europe, mainly due to the Cologne Cathedral, its Romanesque churches and other medieval monuments, more than 2000 years of city history and important international events. Due to the University of Cologne and numerous other universities, Cologne is the largest educational and research center in the West of Germany. It is also an important congress and exhibition venue, among others, the Fotomesse Photokina, the confectionery trade fair and the video games fair Gamescom as world-leading trade fairs and the Art Cologne as one of the oldest art fairs in the world.