After this, the Huguenots (with estimates ranging from 200,000 to 1,000,000) fled to Protestant countries: England, the Netherlands, Switzerland, Norway, Denmark, and Prussia—whose Calvinist Great Elector Frederick William welcomed them to help rebuild his war-ravaged and underpopulated country. Following this exodus, Huguenots remained in large numbers in only one region of France: the rugged Cévennes region in the south. There were also some Calvinists in the Alsace region, which then belonged to the Holy Roman Empire of the German Nation. In the early 18th century, a regional group known as the Camisards (who were Huguenots of the mountainous Massif Central region) rioted against the Catholic Church, burning churches and killing the clergy. It took French troops years to hunt down and destroy all the bands of Camisards, between 1702 and 1709.