In the 1850s, large numbers of United States citizens arrived, most usually after periods in gold rush California. These migrants settled predominantly in rural Victoria, where the discovery of gold had encouraged a large colony of prospectors and speculators. A number of United States-born played eminent roles in the Eureka Stockade, particularly in regard to paramilitary formations organised for self-defence by the miners. The colonial authorities suspected the United States-born – amongst others, such as the Irish – of disseminating republicanism.