These “fish tags” get their name from their shape. The wood tags were carved with an identifying ideograph and then split in two. Putting the two halves together so they fit perfectly proved the authenticity of the holder. In Sui and Tang dynasty China, the tags served as proof of identity and authority. Only royals and the highest-ranking officials could use them. As a result, matching up a tag lent the person the right to pass through closed gates into restricted areas and to lead an army into battle.