The simplest forge, known as the Corsican, was used prior to the advent of Christianity. Examples of improved bloomeries are the Stuckofen, sometimes called wolf-furnace,) which remained until the beginning of the 19th century. Instead of using natural draught, air was pumped in by a trompe, resulting in better quality iron and an increased capacity. This pumping of air in with bellows is known as cold blast, and it increases the fuel efficiency of the bloomery and improves yield. They can also be built bigger than natural draught bloomeries.