Sultanahmet Square is the main square of Istanbul, located in the historical center of the city in Sultanahmet, Fatih district. It consists of two parts: the square between the St. Sophia Cathedral and the Blue Mosque and the Hippodrome square itself, where the columns and obelisks installed during the Byzantine period and the German Fountain, donated to the city and Sultan Abdul Hamid II by Kaiser Wilhelm II, have survived. The square was named after the Sultan Akhmet (Blue Mosque) mosque, located on it. Part of Sultanahmet Square is located on the site of the ancient Hippodrome, the construction of which was begun by the Roman emperor Septimius Severus in the north in 203, when the city was called Byzantium. In 330–334, the emperor Constantine, creating a new capital, completely rebuilt the Hippodrome. After the restructuring, the size of the structure was about 450 meters long and 120 meters wide, the capacity of the racetrack was about 100,000 people. The entrance to the hippodrome was on the north side, approximately where the German fountain is now installed. Hippodrome decorated the famous quadriga, exported in 1204 to Venice. Chariots races were held on the racetrack, which in their intensity of passion led to major fights among fans, and sometimes riots. Fans of spectacles (gladiatorial battles, and then, with the introduction of Christianity - circuses and hippodromes) both the old Roman and Eastern empires were divided into several groups by color, in particular, the chariots, for which they were sick and which they contained: red, white, blue, green. For several centuries, the two major categories — blue (venety) and green (prasiny) —are the largest and most influential. After the conquest of Constantinople by the Turks in 1453, the Hippodrome was used only as a venue for various performances, fairs and other entertainment events. Janissaries organized here protests and presentations. In the 15-16 centuries, the building was gradually dismantled for the construction of the Topkapı and Ibrahim Pasha Palaces, as well as the foundation of the Sultan Ahmet mosque. Sfendon facilities remained intact, but the windows in it the Turks laid a brick. Surveys found in the Sfendon huge empty rooms, partially filled with groundwater. Also found were underground tunnels leading to the Ibrahim Pasha Palace and Topkapi below the surface of Sultan Ahmet Square.