It is believed that Jethavanaramaya(Jetavana Stupa) is the work of King Mahasen in the 4 th Century. The dagaba was originally built to a height of 400 feet being the third largest building in the world during that time. The chronicles state that Jetawanaramaya illustrates clearly the way in which the different Buddhist sects which the kings of Anuradhapura followed, and how this had influenced the political affairs of Sri Lanka . The dagaba is stated to have a concrete base and foundations of brick 26 feet deep. When you enter the dagaba from the eastern gateway the Vahalkada has an excellent stele showing a Naga King and an unidentified goddess.
The Jetawanarama monastery clustered around the dagaba includes all the features of a large monastery.(source http://www.anandaloka.org)