'Lankaramaya', Anuradhapura, Sri Lanka.

‘Lankarama is a stupa built by King Valagamba, in an ancient place at Galhebakada in the ancient kingdom of Anuradhapura, Sri Lanka. Nothing is known about the ancient form of the stupa, and later this was renovated. The ruins show that there are rows of stone pillars and it is no doubt that there has been a house built encircling the stupa (vatadage) to cover it. The round courtyard of the stupa seems to be 10 feet (3 m) above the ground. The diameter of the stupa is 45 feet (14 m). The courtyard is circular in shape and the diameter is 1332 feet (406 m)’.

en.wikipedia.org/wiki/Lankarama‎

‘Originally, the Lankarama Dagoba had a conical roof covering that is now long gone. This building is identified as the Silasobbhakandaka Cetiya built by King Valagamba, who went into hiding after being defeated by the Tamils. 

There are three concentric circles of columns around the Lankarama Dagoba. As in the Thuparama Dagoba, the columns of the Lankarama Dagoba used to support the roof of a vatadage, or circular stupa house’ –

http://www.asiaexplorers.com/srilanka/lankarama_dagoba.htm