File:Epidauros Sanctuary - Tholos or Thymele - 4th century BC - 52042701980.jpg

English: The Tholos (or Thymele) was built as part of the major process of monumentalisation in the 4th century around the same time as the temple, altar, and abaton. It was designed by Polykleitos the Younger, who also designed the Theatre. Construction began around 360 BC, however it took some 27 years to build. It is the most elaborate structure at Epidaurus, and was built with the highest quality materials and workmanship. The cost of its construction was approximately twice that of the nearby Temple of Asclepius. Original accounts of its construction refer to the building as the Thymele, which is generally an altar with a hearth for burnt offerings, and no such facility was found in relation to the structure at Epidaurus. Pausanias referred to the building as the Tholos and recorded the beautiful paintings displayed within as well as steles displaying the names of those healed by Asclepius. The extensive list of healing powers included curing blindness, epilepsy, indigestion, baldness, and difficulties with pregnancy. The stele also described former sceptics who were cured, and the various rewards offered to Asclepius in thanks.

Early modern interpretations suggested that the Tholos might have signified the tomb of the god Asclepius with the central portal used as a pit for chthonic offerings to the god, or alternatively as a pit to house snakes. More recent interpretations based on the acoustics of the circular room suggest it was used for musical performances. Music was part of the healing process at Epidaurus, and an inscription of musical notation was found to the west of the Tholos (towards the Palaestra). Although its actual purpose remains unknown, the Tholos was clearly one of the major cult buildings in use during the Classical and Hellenistic periods. The Tholos was constructed as a fully circular building with a diameter of 21.3 metres. It had an outer colonnade of 26 Doric columns, with a second, inner colonnade of 14 Corinthian columns. The structure had an enclosed roof with the frieze and metopes featuring colourfully painted rosettes and floral images. The roof was finished in marble tiles with a decorative gutter and carved marble lion heads for waterspouts. The door architraves were also made of marble and decorated with floral ornaments. The crepidoma had three high steps, with the entrance from the east via a ramp. The internal floor was paved with an inlay of black and white marble rhomboids. A hole in the centre of the structure was covered by a removable slab. It gave access to a complex labyrinthine foundation beneath the Tholos. The labyrinth had a diameter of 13.4 metres and was composed of three concentric circles. Stone barriers and doorways guided movement through the maze of corridors and required a zig-zagging passage to reach the outer corridor. No pottery or other evidence of offerings were found within the underground labyrinth and its purpose is unknown.

The Tholos has been partially restored to show the arrangement of the huge columns and the circular labyrinth below ground. Work is ongoing, however the three stepped crepidoma and entry ramp have been restored, and several columns are partially standing. Four inscribed steles mentioned by Pausanias have been recovered and are on display in the museum.