The mantou kiln or horseshoe-shaped kiln was the most common type of pottery kiln in north China, in historical periods when the dragon kiln dominated south China; both seem to have emerged in the Warring States period of approximately 475 to 221 BC. It is named after the Chinese mantou bun or roll, whose shape it resembles; the ground plan resembles a horseshoe. The kilns are roughly round, with a low dome covering the central firing area, and are generally only 2 to 3 metres across inside. However it is capable of reaching very high temperatures, up to about 1,370 °C (2,500 °F). There is a door or bricked-up opening at the front for loading and unloading, and one or two short chimneys at the rear.