Sandakada pahana is an elaborately carved semi-circular stone slab, usually placed at the bottom of staircases and entrances and is a unique feature of the Sinhalese architecture of ancient Sri Lanka. It symbolises the cycle of Samsara in Buddhism. Anuradhapura is one of Sri Lanka's ancient capitals and famous for its well-preserved ruins. From the 4th century BCE until the beginning of the 11th century CE it was the capital. During this period it remained one of the most stable and durable centers of political power and urban life in South Asia. The ancient city, considered sacred to the Buddhist world, is today surrounded by monasteries covering an area of over sixteen square miles (40 km).