of the ground below sea level, due to bradyseism, seems to have occurred in two phases: between the third and fifth centuries, still in the late Imperial era, followed by a more substantial submersion a century later. The lower part of Baiae was largely submerged by the sea by the 8th century. A cache of plaster casts of Hellenistic sculptures was discovered in the cellar of the Baths of Sosandra at Baiae; they are now displayed at the town's archaeological museum. The collection includes parts of several famous sculptures, including Athens's Harmodius and Aristogeiton and the Athena of Velletri. It suggests that the area had a workshop mass-producing marble or bronze copies of Greek art for the Italian market. Monuments Among the most significant and remarkable remains are several dome-like structures such as the great so-called Temple of Mercury, the Temple of Venus, and the Temple of Diana, which were traditionally credited to some of the more famous residents of the town's villas, (although they were not temples but parts of thermal baths). Temple of Diana This colossal ogival dome, today half collapsed, originally collected vapours coming from the ground below and was used for thermal baths. It was decorated with marble friezes depicting hunting scenes. Temple of Mercury The so-called "Temple of Mercury" contains a large diameter dome, the largest in the world prior to the construction of Rome's Pantheon in 128 AD. The dome has a central hole or oculus, four square skylights, was made with large tuff blocks, and is the oldest known surviving dome made of concrete. Built in the 1st century BC during the late Roman Republic, it was used to enclose the frigidarium or cold pool of the public baths. From the eighteenth century descriptions it appeared to have had six niches of which four were semicircular. Temple of Venus Another octagonal building, sunken 3 metres in the ground, had eight large arched windows and a balcony inside overlooking the pool. It owes its name to Scipione Mazzella who claimed to have found the statue of the goddess there. Villa of the Ambulatio Overlooking the sea is the "Villa of the Ambulatio" with a series of six terraces connected to each other by a complex of staircases of which the last leads to the "sector of Mercury". It is named after the 'ambulatio', the long corridor with two longitudinal naves on the second terrace,