Open fire systems had three significant disadvantages that prompted an evolutionary series of improvements from the 16th century onwards: it was dangerous, it produced much smoke, and the heat efficiency was poor. Attempts were made to enclose the fire to make better use of the heat that is generated and thus reduce the wood consumption. An early step was the "fire chamber": the fire was enclosed on three sides by brick-and-mortar walls and covered by an iron plate. This technique also caused a change in the kitchenware used for cooking, for it required flat-bottomed pots instead of cauldrons. The first design that completely enclosed the fire was the 1735 "Castrol stove", built by the French architect François de Cuvilliés. This stove was a masonry construction with several fire holes covered by perforated iron plates and was also known as a "stew stove". Near the end of the 18th century, the design was refined by hanging the pots in holes through the top iron plate, thus improving heat efficiency even more.