WE WERE standing outside the Corn Exchange, a large public building in Bristol. Beside us stood the Nails, a row of four bronze posts. These flat-topped posts were originally used as trading tables for financial deals in an arcade known as the Merchants' Tolzey. They were cast, one by one, in the 16th and 17th centuries, as trade increased. Completion of a deal was made by paying cash upon the Nail. Centuries of use have left the post tops smooth. 'Worn down by the hands of commerce,' noted my assistant.