Outside the walls of Trozen was a sanctuary of Poseidon Phytalmios (of Growth). The legend said that the angry god once inundated the crops with seawater until he yielded to prayers and sacrifices. Overlooking this shrine was a sanctuary of Demeter Thesmophoros, established by Poseidon’s son Althepos. In recognition of his connection with agriculture, the god was offered aparchai, first fruits from the crops. This facet of Poseidon’s personality is unexpected, yet the cult pairing of Poseidon and Demeter is widespread (present in Attica, Argos, Mykonos, and of course, Arkadia). It is likely that Poseidon’s flood was originally a freshwater inundation, for as a god of subterranean forces, he controlled springs and rivers. Having caused a drought at Argos by drying up the springs, he relented and revealed the sources at Lerna to the Danaid Amymone. Aeschylus (Sept. 304–11) names Earth-supporting Poseidon and the rivers, offspring of Tethys, as the deities who pour forth the waters that fructify the earth. Poseidon’s waters nourish the plants, yet too much water just as surely destroys them. Thus Poseidon’s relationship with Demeter was both intimate and adversarial. Argos had a flood legend according to which Poseidon, angry when the land was awarded to Hera, caused an inundation, and the Argive sanctuary of Poseidon Prosklystios (of Surging Water) was located beside that of Pelasgian Demeter.
Ancient Greek Cults by Jennifer Larson; Poseidon at Trozen (and Argos) pg 64
