Historically, the Chinese have feared the Slavs, essentially because of centuries of their eastward expansion. As early as the seventeenth century, they confronted Slavs along China's Amur River. Geographically speaking, the Slavs were centered around Moscow in the western part of the Eurasian landmass, east of the Ural Mountains. Unlike the steep Rocky Mountains in the United States, the Urals tend to be gently sloping, often with extensive rolling hills. Thus these mountains are relatively easy for people to pass over. History says that a Cossacks headman, Yermak, went over the Ural Mountains and conquered the State of Sibir Khan, which he offered to Ivan the Fourth, the sixteenth century Russian Czar. It is said that Sibir Kanh is the origin of the name Siberia.