 The Cistercians are known to have been skilled metallurgists, and knowledge of their technological advances was transmitted by the order.Iron ore deposits were often donated to the monks along with forges to extract the iron, and within time surpluses were being offered for sale.The Cistercians became the leading iron producers in Champagne, from the mid-13th century to the 17th century, also using the phosphate-rich slag from their furnaces as an agricultural fertiliser.