File:The Fountain of Pnyx (Kallirroe) on June 26, 2020.jpg

English: "During the rulership of the tyrant Peisistratus (6th cent. B.C.) the growth of the city's population necessitated the construction of a well-organized system of fresh water to supply the city's needs. An extremely complex water-providing net was opened, subterranean to a great extend, divided into several branches, covering a distance more than 9,500m. The fresh water was led from Hymettus into the town through sealed clay pipes, laid in underground tunnels of stable inclination, necessary for a continuous flow. A certain branch of this network has been traced at the east side of the Pnyx hill and supplied water for more than eight centuries to a system of rock-cut and build cisterns.

Due to the poor state of knowledge of ancient Athenian topography during the beginning of the 20th century, the German excavator W. Doerpfeld described these installations as the "Enneakrounos" fountain of the tyrants and the "Kallirroe" spring. Already by that time, this identification was seriously questioned. Today the most prevalent theory sets "Kallirroe" in the area of the Illisus river, SE of the Olympieion while the "Enneakrounos" is according to the description Pausanias the archaic fountain that has been uncovered in the SE side of the Agora. Nonetheless, the installation of the chamber-like, rock-cut fountain in the east slope of the Pnyx hill, is still conventionally named "Kallirroe". It consists of a rectangular chamber, chiseled into the bedrock with a shallow well across the entrance, where the water was collected. A second subterranean chamber on a lower level is connected to the former with a stepped corridor. By the time of the emperor Hadrian (2nd cent. A.D.) the floor of the first chamber was decorated with an elaborate mosaic.

During the Second World War, the "Kallirroe" was used as a shelter to protect antiquities and the entrance was sealed with concrete." Text: Information board in the close vicinity of the entrance.