Answer: The 'Four Class System' was a legal caste system in the Yuan Dynasty. After the founding of the Yuan regime, Kublai Khan, the first emperor in the Yuan Dynasty, set up this system to consolidate the ruling status of the Mongolian Ethnic Minority, which had a small number with great disparity to the majority Han people.
Large seaworthy vessels first appeared in the Mediterranean Sea, but of course it should be noted that they also appeared elsewhere in the world as well.
