Plovdiv of which are high. Because of these hills, Plovdiv is often referred to in Bulgaria as "The City of the Seven Hills". Plovdiv is host to a huge variety of cultural events such as the International Fair Plovdiv, the international theatrical festival "A stage on a crossroad", the TV festival "The golden chest", and many more novel festivals, such as Night/Plovdiv in September, Kapana Fest, and Opera Open. There are many preserved ruins such as the ancient Plovdiv Roman theatre, a Roman odeon, a Roman aqueduct, the Plovdiv Roman Stadium, the archaeological complex Eirene, and others. The oldest American educational
Plovdiv Arts; and others. The 2009 International Olympiad in Informatics (IOI) was held at the University of Plovdiv "Paisiy Hilendarski", between 8 and 15 August 2009. The 2009 IOI Honorary Patron was Bulgarian President Georgi Parvanov. Between 1875 and 1906, the Zariphios School was one of the local Greek educational institutions that provided elementary and secondary education. Plovdiv Sports Complex consists of Plovdiv Stadium with several additional football fields, tennis courts, swimming pools, a rowing base with a 2 km-long channel, restaurants, and cafés in a spacious park in the western part of the city just south of the Maritsa river.