Siege of Mafeking, 1899-1900. The second Boer War was the longest and costliest Victorian war. Mafeking became a center of the struggle. The strategically located town was besieged by Boers in the first phase of the war, and its garrision managed to hold out against superior numbers for 217 days until relieved. Commanding mostly local troops and police, Colonel Robert Baden-Powell led a brilliant defense. The eventual relief of the siege was a breaking point for the Boer army.