The Hydreion is located beyond the gateway of Hercules, at the north end of Domitian square near the Memmius monument. This fountain installation was in the small area where Curetes Street the Terrace House Street would have intersected. The elongated rectangular basin has been preserved along with a water basin that is located high above the pool. It is thought that the fountain served more than a decorative purpose. With the large amount of traffic along Curetes Street, the water would have been used to keep the street cleaned. It also would have used to wet the stones way during summer months to keep the heatfrom reflecting off of the marble.

The shape of the Hydreion suggested that it may be a nymphaeum, or a monument consecrated to the nymphs. During the Roman period, the fountain would have ceased being a sacred space and would have simply served as a sanctuaries, reservoirs and assembly-room. Nymphaeum after the Agustian period were often built with a semi-circular apse crowned by a half-cupola like the architectural elements shown by the Hydreion.

The fountain is flanked by four columns which have been re-erected. These columns would have supported four statues in a semi-circular niche. The statues were ordered by Diocletian in the 2^nd century AD when he became Emperor of the East and selected Maximian as Emperor of the West. They would have depicted Diocletian and Maximian along with Galerius and Constantius Chlorus, the men who served as their Caesars. There are indications that fountain repairs took place in the 4^th century AD.

An inscription on the fountain claims that the Hydreion was built in the Severan period, around the year 200 AD, and names T. Flavius Meander as the founder. Reused building elements indicate that the site may have housed a previous monument in the early Imperial period.