The oldest preserved building in Sofia is located in the courtyard of the Presidency. This is the rotunda St. George the Victorious, which was in the heart of the ancient Konstantine neighborhood. In its framework was the location palace of the Roman emperor Constantine the Great and noble house of his subjects. The rotunda is part of an archaeological complex, and scientists today are still arguing about the date of its construction (3^rd to 4^th century). It was mainly used for baptisms but over the years served also as a public building. Because of the presence of remains of an ancient heating system, some archaeologists believe it may have served as a bathroom, as well. The building has retained almost entirely the appearance since its establishment until today, because of which it is considered to be the oldest preserved building in the capital. Its dome was destroyed twice - during the invasion of the Huns and during the Bulgarian siege led by Khan Krum.