21 August 1900
On 21 August 1900 the Boers and the British again clashed in what became known as the battle of Dalmanutha (Bergendal). The battle lasted six days, ending on the 27th of August when the Boers retreated. This was the last conventional battle of the South African War (1899-1902). The climax of the battle of Dalmanutha came on the last day, when 70 men of the Johannesburg Zuid-Afrikaansche Rijdende Politie (ZARP), a special mounted police corps of the Zuid-Afrikaansche Republiek (ZAR) or the Transvaal Republic, faced a full attack by General Sir Redvers Buller's Natal Field Army (also known as the Natal Field Force). By 24 September the entire Transvaal south of Delagoa Bay railway was under British control.  
References

Pretorius F. ‘The Second Anglo-Boer War: An Overview’, in the South African Journal of Military Studies, Vol. 30, (2000)

Jooster C. ‘The Battle of Bergendal’, in the South African Military History Journal, Vol. 12 No 4, (December 2002)|

Melrose House, ‘FROM BLOEMFONTEIN TO PRETORIA’, [online], available at www.melrosehouse.co.za(Accessed: 13 July 2012)|

Heritage History, ‘Boer Wars’, [online], available at www.heritage-history.com (Accessed: 13 July 2012)