Before building of Anitkabir, Anittepe’s (Monument Hill ) name was Rasattepe (Observation Hill) because there was an observatory on this hill.
There were also tumultuous (graves) belonging to Phrygian civilization of 3rd Century BC on this hill. Archaeological excavations took place to remove these tombs after the decision was given to build Anitkabir on Rasattepe. Remains found on these excavations are on display in the museum of Anatolian Civilizations.
The first stage to start the construction was the expropriation of the land after deciding on the Anitkabir project. Actual construction of Anitkabir commenced on 9 October 1944 with a splendid ceremony by laying the first stone of the foundation. Construction of Anitkabir took nine years in four stages. Second stage construction, comprising the mausoleum and the auxiliary buildings surrounding the ceremonial ground, started on 29 September 1945 and completed on 8 August 1950.
The third stage was comprising the construction of the roads leading to the mausoleum, Lions’ alley, ceremonial ground, the mausoleum’s upper-level stone pavement, grand stairs, putting the big tomb stone in its place and installation of electricity, plumbing and heating systems.
https://www.ktb.gov.tr/EN-103960/ankara---anitkabir-ataturks-mausoleum.html