In the east, the rapid Russian exploration and colonisation of vast Siberia was led mostly by the Cossacks, hunting for valuable furs and ivory. Russian explorers pushed eastward primarily along the Siberian River Routes, and by the mid-17th century, there were Russian settlements in eastern Siberia, on the Chukchi Peninsula, along the Amur River, and on the coast of the Pacific Ocean. In 1648, Fedot Popov and Semyon Dezhnyov, two Russian explorers, discovered the Bering Strait, and became the first Europeans to sail to North America.