In ancient China, coins were the main forms of currency from the last phase of the Spring and Autumn Period (770 BC - 476 BC) onward. Coins were made of copper, iron, lead, gold and silver in different shapes, weight and marks. Before that, early Chinese used shells as a medium of exchange in commerce.
Due to their pleasing appearance and being easy to carry and count, shells were the first kind of primitive money circulated at the end of the Neolithic Age. The unit of shell money is "peng" (?, meaning "friend") which originally referred to two clusters of ten shells. Due to the lack of shells in Northeast China at the end of the Shang Dynasty (1675 BC–1029 BC), "shell" money began to be made of pottery, stone, bone, jade, copper and gold. The spread of "shell" money made of copper marks the beginning of the use of metal coins in China. The Warring States Period (475 BC to 221 BC) saw a rise in "huan cash" (??, a kind of ancient copper coin with ring shape). By the end of the Qin Dynasty (221 BC–206 BC), copper coins called "ban liang qian" (? ??) were the mainstream form of currency.