 Fundamental commodities such as grain, rice, and cloth were used and later knives were introduced with settlers coming in from China during the Warring States Period (475 BC - 221 BC) based on archaeological evidence excavated at sites in the Pyongan and Cholla provinces.The Chinese also introduced coins to Korea when the Han dynasty invaded the north at the end of the 2nd century BCE.These coins became the official currency and were known as wuzhu in Chinese or oshuchon in Korean, meaning 'five-grain'.