A considerable amount of traditional arts and crafts is produced by the Banyarwanda, although most originated as functional items rather than purely for decoration. Woven baskets and bowls are especially common. "Imigongo", a unique cow dung art, is produced in the southeast of Rwanda, with a history dating back to when the region was part of the independent Gisaka kingdom. The dung is mixed with natural soils of various colours and painted into patterned ridges to form geometric shapes. Other crafts include pottery and wood carving. Traditional housing styles make use of locally available materials; circular or rectangular mud homes with grass-thatched roofs (known as "nyakatsi") are the most common. The government has initiated a programme to replace these with more modern materials such as corrugated iron.