Klepsydra, North Slope of the Acropolis
The slopes of the Acropolis were home to several sanctuaries that played a vital role in the religious lives of the ancient Athenians. Some of these places, especially on the South Slope, received monumental, architectural embellishments (for example, the sanctuary and Theater of Dionyssos, or the Sanctuary of Asclepios). But many shrines on the slopes were much simpler in nature, of the sort that scholars sometimes call "rustic", and were places where divinities of nature, fertility, and healing were worshiped on a less monumental and more personal level.
This type of "popular" religion is attested vividly on the North Slope of the Acropolis, where many shrines were nestled among the steep cliffs, caves, and pathways. For example, at the northwest corner of the North Slope, Apollo, Pan, and (probably) the Nymphs were worshiped in shallow caves.
On the NW side of the Sacred Rock there is a cut in the rock and stairs leading to several natural caves and to The Klepsydra Spring House, the natural water spring of the rock of the Acropolis, mentioned in Aristophanes' Lysistrata (910-913) and other ancient literary sources. It was also probably sacred to a nymph (originally called Empedó).
This is a spring with a history going back into prehistoric times. That there was a supply of water in the area appears to have been known as early as the Neolithic period. The first fountain house, however, was built here much later, in 470-460 B.C., perhaps by the renowned Athenian politician Kimon. It was a simple rectangular construction, with a built-in draw-basin next to the spring. The north part had a paved court for collecting rain water from the north slope of the Acropolis.
Located at the intersection of the Panathenaic Way with the Peripatos, Klepsydra was initially approachable only from outside the Acropolis by way of a stairway leading from the ground level down to the lower level of the spring.
During the 3rd century A.C., however, a succession of landslides damaged the spring and blocked the entrance, so that the only means of approach was by a stairway that began behind the Agrippa Monument at the Propylaia. Water was now drawn from a well over which was a vaulted roof. Klepsydra continued being used during the Byzantine times and the Frankish domination.
Farther to the east, Eros and Aphrodite had an open-air sanctuary. Evidence for other shrines is provided by numerous rock-cut niches for the dedication and display of offerings to gods whose names we do not know. The sacred spots on the slopes of the citadel were connected by an ancient path, called the Peripatos, that circled the Acropolis and intersected the Panathenaic Way at the western approach. It is also likely that most (if not all) of the North Slope was within the sacred area at the foot of the Acropolis known as the Pelargikón.