Ankara Treaty of Lausanne (1923), the Turkish nationalists replaced the Ottoman Empire with the Republic of Turkey on 29 October 1923. A few days earlier, Ankara had officially replaced Constantinople as the new Turkish capital city, on 13 October 1923. After Ankara became the capital of the newly founded Republic of Turkey, new development divided the city into an old section, called "Ulus", and a new section, called "Yenişehir". Ancient buildings reflecting Roman, Byzantine, and Ottoman history and narrow winding streets mark the old section. The new section, now centered on Kızılay Square, has the trappings of a more modern city:
Altındağ, Ankara remains one of the poorer quarters of the capital. The hillside is covered with illegally built gecekondu housing, home to low-income families. Among the housing there are some municipal buildings, public housing, state housing for civil servants and lots of small workshops doing car repairs and other light mechanical work. The ancient Ankara Castle is in Altındağ and there has recently been investment in restoration work. With this architectural heritage, Altındağ is a member of the Norwich-based European Association of Historic Towns and Regions. Altındağ includes parts of the historic city of Ankara, as well as the first National Assembly