18 May 1902
Boer negotiators travelled from Vereeniging to Pretoria to present their proposals for surrender to British representatives,  Lord Milner and Lord Kitchener. They were still asking for a continued independence of the Boer republics. This happened towards the end of the Anglo-Boer War II which broke out in October 1899. It ended with the signing of the Peace Treaty of Vereeniging on 31 May 1902.
References

Boddy-Evans, A. ‘This Day in African History: 18 May 1902’, from About African History, [online], available at https://africanhistory.about.com (Accessed: 19 April 2013)|

Anglo-Boer War Museum, ‘Peace Treaty of Vereeniging’, [online], available at www.anglo-boer.co.za (Accessed: 19 April 2013)