Towards the end of the Roman Republic, the ancient Roman city of Baia, located on the west coast of the Gulf of Puteoli or Pozzuoli, and 16 km west of Naples, was a fashionable resort preferred by the wealthy Romans. As the city was located over natural volcanic vents, it had plenty of healing medicinal hot springs, which made it more preferable than Capri, Pompeii, and Herculaneum to the affluent Romans, who built their personal villas in the town from 100 BC to 500 AD. For centuries, Baia served the recreational whims of the famous, rich, and powerful Roman elites, and was notorious for the hedonistic lifestyle of its residents and guests, along with the associated rumors of corruption and scandals.

Traditionally, Baia was named after Baios, the helmsman of Ulysses or Odysseus, but in 178 BC, it was mentioned as Aqua Cumanae due to the presence of the curative sulfur springs. The mild climate of the city, luxuriant vegetation, associated with the thermal springs made it a popular resort, and by the 1st century, it became as large as Pozzuoli, a leading commercial centre in those days.

During the last phase of the Roman Republic many famous and powerful figures like Roman general Gaius Marius, Lucius Licinius Lucullus, a politician of the late Roman Republic, and Pompey the great, a leading Roman general and statesman frequented the fashionable city. Julius Caesar had a villa in the city, where Emperor Hadrian died in 138 AD. However, much of the town became imperial property under Caesar Augustus, the first Roman emperor, and Nero also had a luxurious villa built there in the middle of the 1st century.

According to Suetonius, a primary source on Roman history, in 39 AD an astrologer called Thrasyllus predicted that Caligula had no more chance of becoming an emperor than of riding a horse across the Gulf of Baia. To prove him wrong, Caligula ordered to build a three-mile-long pontoon bridge from impounded ships, fastened together and weighted with sand, stretching from Baiae or Baia to Puteoli, and clad in a gold cloak crossed it mounted on a horse. The event is also included in Roman statesman and historian Cassius Dio’s Roman History and few scattered fragments were shown to tourists as the Bridge of Caligula, as late as the 18th century.

However, the golden days of Baia did not last long as it was sacked during the Barbarian Invasions, notably by the German tribes, the Huns, and the early Slavs, which possibly begun in 375 AD, and ended in 568 AD, and again by the Muslims in the 8th century. The formerly luxurious city was finally abandoned by 1500 due to recurrent attacks of Malaria.

Part of the abundant city was gradually swallowed by the sea. In fact, due to the local volcanic activity water level rose through the volcanic vents, which were once an attraction to the city, and more than 328 feet (100 m) of the site became submerged in the bay. It is estimated that the ground was lowered below sea level in two phases between the 3rd and the 5th centuries, still in the late Imperial era, followed by more substantial submersion a century later. However, the lower part of the city was swallowed by the sea by the 8th century.

The important archaeological ruins that were excavated in 1941 include several dome-like structures, the remains of the ancient bathing facilities, which are now referred to as temples. The so-called Temple of Mercury consists of a huge 71 feet (21.5 m) diameter dome, dates from the late Roman Republic, and used to enclose the cool pool of the public baths. The half-collapsed 97 feet (29.5 m) diameter colossal dome of the Temple of Diana, decorated with marble friezes depicting hunting scenes, originally collected steam vapour coming from the ground below and was used for thermal baths.

Another octagonal structure, sunken around 10 feet (3 m) is known as the Temple of Venus as a statue of the goddess was found there, had eight large arched windows and an inside- balcony overlooking the pool. Another octagonal structure, sunken around 10 feet (3 m) in the ground, is known as the Temple of Venus as a statue of the goddess was found there. It had eight large arched windows and an inside balcony overlooking the pool

The sculptures of the completely submerged nymphaeum of Emperor Claudius, consecrated to the nymphs, were shifted to the archaeological museum of the city. Nevertheless the other ancient remains of Baia are carefully preserved in one of the world’s few underwater archaeological parks, which can be viewed through glass-bottomed boats. One can even swim among the crumbled structures and the statuary of the lost city by snorkeling or scuba diving. Although the underwater statues are replicas, they still feel ghostly and sublime.