14 October 1931
On 14 October 1931, Pretoria achieved official city status. The city was established in 1855 by Marthinus Pretorius, a leader of the Voortrekkers who named it after his father Andries Pretorius. Andries Pretorius became a hero of the Voortrekkers after he defeated the Zulus in the Battle of Blood River. The city became the Administrative Capital of the Union of South Africa which was constituted in 1910 with the merger of the Transvaal Colony (former Boer Republic of the ZAR), the Orange Free State Colony (former Boer Republic of the Orange Free State), the Cape Colony and Natal Colony. Thirty years later, in 1961, when the Union of South Africa became completely independent of England and became a republic, Pretoria retained its position of Administrative Capital of the Republic of South Africa. While Johannesburg was the scene of many dramatic incidents, Pretoria was the place where apartheid was actually administered from.
References

Pretoria.co.za (2011). ‘History’ from City of Tshwane Pretoria: History [online] Available at www.pretoria.co.za [Accessed 02 September 2011]|

Visitpretoria.co.za (2011). ‘History of Pretoria’ from Visit Pretoria: Visitors Guide to Pretoria [online] Available at www.visitpretoria.co.za [Accessed 26 September 2011]