The Jetavanarama stupa or Jetavanaramaya is a stupa, or Buddhist reliquary monument, located in the ruins of Jetavana monastery in the UNESCO world heritage city of Anuradhapura, Sri Lanka.

It was built by King Mahasena of Anuradhapura (273–301). At that time, It was the world's tallest stupa and the third tallest structure in the world at 122 meters. He initiated the construction of the stupa  following the destruction of the Mahaviharaya of Anuradhapura. His son Maghavanna I completed the construction of the stupa, and was renovated by Parakramabahu I of Polonnaruwa. A part of a sash or belt tied by the Buddha is believed to be the relic that is enshrined here.

The compound covers approximately 5.6 hectares and is estimated to have housed 10,000 Buddhist monks. One side of the stupa is 176 m long, and the flights of stairs at each of the four sides of it are 9 m wide. The doorpost to the shrine, which is situated in the courtyard, is 8 m high. The stupa has a 8.5 m deep foundation, and sits on bedrock.

The foundations of the structure were 8.5m deep and the size of the structure required bricks which could withstand loads of up to 166 kg. The solid foundation lay on bed-rock and the dome was constructed of full and half bricks and earth fill, the unique shape of a perfect ellipsoid allowed for stress and thus allowed the construction of the large structure.

Finely crushed dolomite, limestone, sieved sand and clay provided the bonding material for the bricks. The clay employed was pliable and thus accommodates movement within the structure. One of the sides of the brick was roughened to trap the bonding slurry thus limiting lateral movement. The stupa was then covered with lime plaster; the plaster used contained seashells, sugar syrup, egg whites, coconut water, glues, oils, plant resin, sand, clay and pebbles. The plaster also provided waterproofing for the structure. The Mahavamsa also mentions the use of copper sheets over the foundation and arsenic dissolved in sesame oil to prevent insect and plant intrusions inside the stupa. It is estimated that Jetavanaramaya took 15 years to complete and would have required a skillful workforce of hundreds, including brickyard workers and bricklayers, and stonemasons.

The structure is no longer the tallest, but it is still the largest, with a base-area of 233,000 m2. Approximately 93.3 million baked bricks were used in its construction; the engineering ingenuity behind the construction of the structure is a significant development in the history of the island.

The structure is significant in the island's history as it represents the tensions within the Theravada and Mahayana sects of Buddhism; it is also significant in recorded history as one of the tallest structures in the ancient world, and the tallest non-pyramidal building. The height of the stupa was 122 metres, making it the tallest stupa in the ancient world.

According to wikipedia