With the guerrillas requiring supplies , Koos de la Rey lead a force of 3 @,@ 000 Boers against Brakfontein , on the Elands River in Western Transvaal . The post held a large quantity of stores and was defended by 300 Australians and 200 Rhodesians . The attack began on 4 August 1900 with heavy shelling causing 32 casualties . During the night the defenders dug in , enduring shelling and rifle fire . A relief force was stopped by the Boers , while a second column turned back believing that the post had already been relieved . The siege lasted 11 days , during which more than 1 @,@ 800 shells were fired into the post . After calls to surrender were ignored by the defenders , and not prepared to risk a frontal attack , the Boers eventually retired . The Siege of Elands River was one of the major achievements of the Australians during the war , with the post finally relieved on 16 August .