In 1898, diamonds were discovered on farms near Pretoria, Transvaal. One led to the discovery of the Premier Mine. The Premier Mine was registered in 1902 and the Cullinan Diamond, the largest rough diamond ever discovered, was found there in 1905. (The Premier Mine was renamed the Cullinan Mine in 2003). However, its owner refused to join the De Beers cartel. Instead, the mine started selling to a pair of independent dealers named Bernard and Ernest Oppenheimer, thereby weakening the De Beers stronghold.