Wikipedia
A vatadage s a type of Buddhist structure found in Sri Lanka. It also known as a dage, thupagara and a cetiyagara. Although it may have had some Indian influence, it is a structure that is more or less unique to the architecture of ancient Sri Lanka. Vatadages were built around small stupas for their protection, which often enshrined a relic or were built on hallowed ground. Circular in shape, they were commonly built of stone and brick and adorned with elaborate stone carvings. Vatadages may have also had a wooden roof, supported by a number of stone columns arranged in several concentric rows.
Only ten vatadages now remain in Sri Lanka. The builders of many of these monuments are unknown, as are their time of creation. The oldest such construction is believed to be the one surrounding the Thuparamaya. The best example of a vatadage is generally believed to be the Polonnaruwa Vatadage. Along with it, the vatadages at Medirigiriya, and Tiriyaya remain more or less intact.