The Orle d'Or Tower, cracked in many places, once formed part of Semur Castle, dismantled in 1602. It owes its name to the battlements (removed), once covered with coppered lead ("un ourlet d'or", a gold rim). Its dimensions are impressive: height 44m, walls 2.20m thick at the top, 5m at the base. Before Pont Joly was built (1787), the Orle d'Or Tower was also one of the gateways into town. Today, it houses the headquarters of Semur's Society of historical and natural science.