The Heidelberg Tun (German: Großes Fass), or Great Heidelberg Tun, is an extremely large wine vat contained within the cellars of Heidelberg Castle. There have been four such barrels in the history of Heidelberg. In 1751, the year of its construction, the present one had a capacity of 221,726 litres (58,574 U.S. gallons). Due to the drying of the wood its current capacity is 219,000 litres (57,854 U.S. gallons). One hundred and thirty oak trees were reputedly used in its construction. It has only rarely been used as a wine barrel, and in fact presently enjoys more use as a tourist attraction, and also as a dance floor since one was constructed on top of the tun.