Traditional Fijian homes or bures are usually built communally by members of the same mataqali. The main wooden structure is made from a hardwood tree, often vesi. Bure shapes vary slightly between regions: most are broadly rectangular although in Lau they have rounded ends similar to those found in Tonga. The wooden posts are joined together with magimagi, a fibrous coconut string, rather than nails or bolts. There is no central post, ensuring a large open-plan living area and a high ceiling for ventilation. The walls are usually made from bamboo, sliced and woven together. A raised platform makes up the floor, and this is laid with straw as a cushion and woven mats for decoration. The roof is thatched using a reed called sina and lasts for around five years before being replaced. Across the top of the roof, or piercing either side, is a black post known as the balabala. This is the trunk of a fern tree and is decorated with white cowrie shells to indicate various forms of chiefly status. Roofs of lesser huts or kitchens are made from the leaf of the coconut tree and will last from three to ten years depending on the skill in weaving. Bures are usually laid out around a central rara, or village green, used for ceremonial events and daily rugby practice.