Following the Ottoman defeat at World War I, the Ottoman capital Constantinople (modern Istanbul) and much of Anatolia were occupied by the Allies, who planned to share these lands between Armenia, France, Greece, Italy and the United Kingdom, leaving for the Turks the core piece of land in central Anatolia. In response, the leader of the Turkish nationalist movement, Mustafa Kemal Atatrk, established the headquarters of his resistance movement in Ankara in 1920. After the Turkish War of Independence was won and the Treaty of Svres was superseded by the Treaty of Lausanne, the Turkish nationalists replaced the Ottoman Empire with the Republic of Turkey on 29 October 1923.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 Yeniehir. Ancient buildings reflecting Roman, Byzantine, and Ottoman history and narrow winding streets mark the old section. The new section, now centered on Kzlay Square, has the trappings of a more modern city: wide streets, hotels, theaters, shopping malls, and high-rises. Government offices and foreign embassies are also located in the new section. Ankara has experienced a phenomenal growth since it was made Turkey's capital in 1923, when it was "a small town of no importance". In 1924, the year after the government had moved there, Ankara had about 35,000 residents. By 1927 there were 44,553 residents and by 1950 the population had grown to 286,781. Ankara continued to grow rapidly during the latter half of the 20th century and eventually outranked Izmir as Turkey's second largest city, after Istanbul. Ankara's urban population reached 4,587,558 in 2014, while the population of Ankara Province reached 5,150,072 in 2015.
The foundations of the Ankara castle and citadel were laid by the Galatians on a prominent lava outcrop (39.941N 32.864E / 39.941; 32.864), and the rest was completed by the Romans. The Byzantines and Seljuks further made restorations and additions. The area around and inside the citadel, being the oldest part of Ankara, contains many fine examples of traditional architecture. There are also recreational areas to relax. Many restored traditional Turkish houses inside the citadel area have found new life as restaurants, serving local cuisine.
The citadel was depicted in various Turkish banknotes during 19271952 and 19831989.