The springs and fountains of the Acropolis hill
O n the north slope of the Acropolis, inside the cave of Ersis (until recently it was attributed to the nymph Aglauros), an impressive structure exists for a spring that was probably discovered during the fortification works of the Acropolis (Pelargikon or Pelasgikon wall, second half of 13th century BC) for the protection against imminent invasion by the Dorians.
The spring construction, in use only for a short time during the Mycenaean period, is believed to be one the first technical works to ensure water supply to the city. Mycenaean pottery found in it, dating from the second half of the 13th century BC and not later indicates the period of use that was not longer than 30-40 years. In all probability a landslide or earthquake must have blocked it.
The entrance to the cave is at the level of the Parthenon, west of the Arrhephorion, a small square building where young women (Arrhephoroi) used to weave the mantle/veil of the goddess (Athena) for the Panathenaic festival and other rituals.
The cave is an impressive, almost vertical fissure, 35m deep, with a series of stairways. In the upper part the rock was carved in order to support wooden steps; while in the lower part the stairways were made using large schist slabs placed on rubble, which was supported by wooden beams.
The stairway ended at the boundary between the upper layer of limestone rock and the underlying layer of marl rock. In this lower part of the cave there was a well, 9m deep, that provided access to an underground vein of water. The diameter of the well was ~ 2m at the surface and 4m near the bottom.
The spring ceased to be in use, as its lower part was covered with soil probably due to an earthquake or landslide. However, the upper part of the cave remained intact and as it has a second exit to the north slope of the rock it was used during antiquity, and in subsequent periods, as a secret passage. Actually, this passage is linked to a heroic moment of recent Greek history. During the Nazi occupation in 1941 two students Manolis Glezos and Apostolos Santas used this passage to reach the Acropolis and take down the Nazi flag.