The technique was developed in Wallonia in present-day Belgium during the Middle Ages. The Walloon method  consisted of making pig iron in a blast furnace, followed by refining it in a finery forge. The process was devised in the Liège region, and spread into France and thence from the Pays de Bray to England before the end of the 15th century.  Louis de Geer took it to Roslagen in Sweden in the early 17th century, where he employed Walloon ironmakers.  Iron made there by this method was known in England as oregrounds iron.