5) Temple of Diana

5. Temple of Diana

Located near the former Cumana railway station in Baia, it is actually a vast domed thermal hall. Today, only half of it is visible due to the rising ground, but its internal ogival structure is a testament to Roman engineering in managing thermal steam.

The so-called "Temple of Diana" is one of the most imposing and visually striking structures in all of Baia, located near the current train station. Despite its traditional name, it is not a religious building, but a colossal thermal hall that was part of the "lower" baths complex. Its architecture is an extraordinary testament to the evolution of the Roman dome. The building features an octagonal plan on the outside that transitions into a pointed dome on the inside, anticipating by centuries architectural solutions that would only be seen in the Gothic and Renaissance periods.

Today, the temple appears partially buried: due to bradyseism and erosion of the soil from the hill behind it, the original floor level is approximately 10 meters below the current street level. This partial "burial," however, has helped preserve the wall structure. When viewed from the interior (when accessible) or from nearby vantage points, one notices the majesty of the vault, which was once entirely covered in precious marble and mosaics that reflected the light coming from the large thermal windows. The name "Diana" was attributed by ancient antiquarians to the temple because of some reliefs depicting hunting scenes and wild animals found nearby. Its actual function was a sudatorium, or large passageway between rooms of different temperatures. Its structural grandeur served to impress visitors, reminding them that in Baiae, even the most daring engineering was at the service of physical pleasure and well-being.