Budapest is the capital and the most populous city of Hungary, and the ninth-largest city in the European Union by population within city limits. The city has an estimated population of 1,752,286 over a land area of about . The history of Budapest began when an early Celtic settlement transformed into the Roman town of Aquincum, the capital of Lower Pannonia. The Hungarians arrived in the territory in the late 9th century, but the area was pillaged by the Mongols in 1241–42. Re-established Buda became one of the centres of Renaissance humanist culture by the 15th century. The Battle of Mohács, in 1526, was followed by nearly 150 years of Ottoman rule. After the reconquest of Buda in 1686, the region entered a new age of prosperity, with Pest-Buda becoming a global city after the unification of Buda, Óbuda, and Pest on 17 November 1873, with the name 'Budapest' given to the new capital. Budapest also became the co-capital of the Austro-Hungarian Empire, a great power that dissolved in 1918, following World War I. The city was the focal point of the Hungarian Revolution of 1848, the Battle of Budapest in 1945, and the Hungarian Revolution of 1956. Budapest is an Alpha − global city with strengths in commerce, finance, media, art, fashion, research, technology, education, and entertainment. It is Hungary's financial centre and was ranked as the second fastest-developing urban economy in Europe. Budapest is the headquarters of the European Institute of Innovation and Technology, the European Police College and the first foreign office of the China Investment Promotion Agency. Over 40 colleges and universities are located in Budapest, including the Eötvös Loránd University, the Semmelweis University and the Budapest University of Technology and Economics. Opened in 1896, the city's subway system, the Budapest Metro, serves 1.27 million, while the Budapest Tram Network serves 1.08 million passengers daily. The central area of Budapest along the Danube River is classified as a UNESCO World Heritage Site and has several notable monuments, including the Hungarian Parliament and the Buda Castle. The city also has around 80 geothermal springs, the largest thermal water cave system, second largest synagogue, and third largest Parliament building in the world. Budapest attracts around 12 million international tourists per year, making it a highly popular destination in Europe. The city was chosen as the Best European Destination of 2019, a major poll conducted by EBD, a tourism organisation partnering with the European Commission. It also topped the Best European Destinations 2020 list by Big7Media. Budapest also ranks as the 3rd best European city in a similar poll conducted by Which? Magazine.