3 May 1900
In the middle of the South African War II (Anglo-Boer War II), General Lord Roberts left Bloemfontein and began the 'March to Pretoria' with nearly 44,000 men, 18,000 horses, and 1200 field-guns. The War had started eight months earlier due to a number of interrelated factors. These included conflicting political ideologies of imperialism and republicanism, the discovery of gold on the Witwatersrand, tension between political leaders, the Jameson Raid and the Uitlander franchise. The war ended on 31 May, 1902 following the signing of the Peace Treaty of Vereeniging.
References

Boddy-Evans, A. ‘This Day in African History: 3 May’, from About African History, [online], available at https://africanhistory.about.com [Accessed: 11 April 2013]|

Anglo-Boer War Museum, ‘Peace Treaty of Vereeniging’, [online], available, www.anglo-boer.co.za (Accessed: 11 April 2013)|

South African History Online, ‘South African War 1899-1902 | Second Anglo-Boer War’, [online], available at www.sahistory.org.za (Accessed: 11 April 2013)