Castalian Spring: source near the sanctuary of Delphi, dedicated to the god Apollo and the Muses.
The Castalian Spring in Delphi is not in the sanctuary of Apollo itself, but about 500 meters east of its main entrance. According to Euripides' play Ion,note[Euripides, Ion 94ff.] visitors of the oracle went to this source first to ritually cleanse themselves. Washing one's hair was sufficient, although murderers had to wash themselves completely.
The water was also used to sprinkle the temple of Apollo. It came down from the two rocks that were known as the Pheriads, and plunged down as a little stream, the Papaddia, from the rocks, and joined the river Pleistos below Delphi. According to the Greek author Pausanias, the water had a delicious taste.note[Pausanias, Guide to Greece 10.8.5.]
The same author records several ancient traditions about the origin of the name, one of them being that the source was called after a local lady. The Carian poet Panyassis, who is quoted by Pausanias, appears to have called Castalia a daughter of the river Achelous, while others - including the lyrical poet Alcaeus - believed that the spring was connected to the Cephissus river.
According to legend, Apollo planted here a shoot of the laurel that he had brought to Delphi from the Tempe Canyon, which was all that had been left of the woman he loved, Daphne. There may indeed have been an ancient cult for a tree; there appears to have been a statue for Ge, Mother Earth, as well. The Greek researcher Herodotus of Halicarnassus states that close to the Castalian Spring, one could find a sanctuary that was dedicated to Autonous, a local hero who helped to push back the Persian invaders in 480 BCE.note[Herodorus, Histories 8.39.]
Today, one can see a rectangular square basin of about 9x3 meters, hewn out in the hard soil. Next to it is a long reservoir in which the water from the Pheriads was collected, before it was fed to seven jets, which had the shape of lion heads. This monument dates back to the Hellenistic (or Roman) period, and is not the oldest building on the site: a fountain house from the Archaic period has been discovered as well.
The source was well-known throughout the ancient world, and the word "Castalia" could be used as a synonym for Delphi.note[E.g., Pindar, Pythian Ode 4.163.] In the Roman age, the word could be a way to describe poetic inspiration.note[E.g., Virgil, Georgics 3.293.] It could even be a synonym for wisdom, and it is therefore not very surprising to find a representation of the Castalian Spring - which was, when all was said and done, part of a pagan cult - depicted in a Christian church, like the one at Qasr Libya in the Cyrenaica.
The British classicist Peter Levi records, in a footnote to his translation of Pausanias' Guide to Greece that in the 1960s, there was still a believe that Castalia's water was magically medicinal, and that it was privately and secretly bottled for these uses.note[Pausanias' Guide to Greece (1971_ vol. II, page 426.]