The term tholos applies to a beehive structure, often with a hole at the top. They range in size from the size of a personal tomb to grand structures with entrance approaches, such as are seen at Mycenae. They may be tombs or they may be places to summon ghosts of the dead to the surface. They probably have their origin in Africa, where similar huts are seen in tribal villages, housing the remains and ghosts of ancestors. They probably came to Greece by way of Libya.
We have a good personal account of a descent into another oracle, that of Trophonius, by Pausanius. In it is described a descent through a constricted space to visit the oracle, after much preparation. The account may well have close Orphic parallels with the situation at Baia.
‘To descend into the cave of Trophonius’ became a proverbial way of saying ‘to suffer a great fright’, as alluded to in Aristophanes’s ‘Clouds’.
The Baia Tholos
The building here has been converted to a sudatorium, a Roman sweat bath. It is lined with diamond-shaped Neronian opus reticulatum. It shows signs of shape distortion, which may well be due to seismic activity and the earthquake of 63 AD.
It is a 16 foot (4.88 metres) tall and 16 foot (4.88 metres) diameter bottle-shaped building with a 3 foot diameter (0.9 metre) vent in the roof, open to the terrace on the level above. It has a passage at the back which extends for 32 feet (9.75 metres) on a bearing of 245º until it connects to the main oracle tunnel. At this point it is now blocked, but there is a Roman pipe leading through the blockage, which was how the hot steam was pumped in under the floor. The steam did not originate within the tunnels, but was pumped in through the pipe in the shelf which was placed in the trench under the temple.
The vent on the level above has a rim comprised of four curved marble blocks, which Paget surmised were supports for a lid of some kind. The supports are still there and clearly visible on Google maps/earth, open to the sky. There may once have been a domed room above, because we can see the ruin of something like this against the cliff on the upper level.
Google image showing Tholos hole
It is hard not imagine that there was an intentional descent of some kind here, through the hole, down to the passage in the floor and along to meet the main tunnel to oracle complex itself. It would be very similar to a descent account described at the oracle of Trophonius.
The entrance to the Tholos
Although they look resonably well centred, both the doorway and the aperture above it are not exactly true to the axis of the Tholos behind it, which suggests that these openings were not part of the original design and a later Roman addition.
Paget considered the Tholos to be one of the oldest buildings here. The evidence Paget found suggests that the original cliff was at the back of the Tholos. Subsequent rock falls over the centuries brought the cliff forward.
The Cuma Tholos
There is also a Greek Tholos at Cuma nearby, about which little is known. Built with similar cyclopean blocks to those used in the Greek Temple at Baia.
Drawing by G. Pellegrini, 1903.