Other highlights include a total of 80 geothermal springs, the world's largest thermal water cave system, second largest synagogue, and third largest Parliament building. Budapest is the capital and the largest city of Hungary and one of the largest cities in the European Union. It is the country's principal political, cultural, commercial, industrial, and transportation centre. The Budapest Commuter Area is home to 3.3 million people.
The first settlement on the territory of Budapest was built by Celts before 1 AD. It was later occupied by the Romans. The Roman settlement - Aquincum - became the main city of Lower Pannonia in 106 AD. The Romans constructed roads, amphitheaters, baths and houses with heated floors in this fortified military camp. Acquincum is the main and best-conserved of the Roman sights in Hungary. Hungarians led by Árpád settled in the territory at the end of the 9th century, and a century later officially founded the Kingdom of Hungary. The Tatar invasion in the 13th century quickly proved that defence is difficult on a plain. King Béla IV of Hungary therefore ordered the construction of reinforced stone walls around the towns and set his own royal palace on the top of the protecting hills of Buda. In 1361 it became the capital of Hungary.
The cultural role of Buda was particularly significant during the reign of King Matthias Corvinus. The Italian Renaissance had a great influence on the city. His library, the Bibliotheca Corviniana, was Europe's greatest collection of historical chronicles and philosophic and scientific works in the 15th century, and second only in size to the Vatican Library.
The Ottomans pillaged Buda in 1526 and the Turkish occupation lasted for more than 140 years. The Turks constructed many fine bathing facilities within the city. Some of the baths that the Turks erected during their occupation period are still in function after 500 years (Rudas and Király). In 1849 the Chain Bridge linking Buda with Pest was opened as the first permanent bridge across the Danube and in 1873 Buda and Pest were officially merged with the third part, Óbuda (Ancient Buda), thus creating the new metropolis of Budapest. The dynamic Pest grew into the country's administrative, political, economic, trade and cultural hub.
In 1949, Hungary was declared a communist People's Republic. In 1956, peaceful demonstrations in Budapest led to the outbreak of the Hungarian Revolution. This uprising was an anti-Soviet revolt that lasted from 23 October until 11 November. The leadership collapsed after mass demonstrations began on 23 October, but Soviet tanks entered Budapest to crush the revolt. From the 1960s to the late 1980s Hungary was often satirically referred to as "the happiest barrack" within the Eastern bloc, and much of the wartime damage to the city was finally repaired. In the last decades of the 20th century the political changes of 1989–90 concealed changes in civil society and along the streets of Budapest. The monuments of the dictatorship were taken down from public places, into Memento Park.
The city has a humid continental climate, with warm or very warm summers. Winter (November until early March) can be very cold and there is little sunshine. Snowfall is fairly frequent in most years, and nighttime temperatures of −15 °C (5 °F) are not uncommon between mid-December and mid-February. The spring months (March and April) see variable conditions, with a rapid increase in the average temperature. The weather in late March and April is often very agreeable during the day and fresh at night. Budapest's long summer - lasting from May until mid-September - is warm or very warm. Budapest has as much summer sunshine as many Mediterranean resorts.