At that time, coin-casting technology was not well-developed, so private bills are assumed to have been issued when a large amount of low denomination coins were needed for purposes such as payment of workers on construction projects.
当時は貨幣鋳造技術が未発達であり、土木工事などの賃金の支払いで小額貨幣が大量に必要になったときに、これらの私札が発行されたと考えられている。