The sanctuary of Poseidon at Onchestos provides a setting for some of the most ancient events described in Greek myth. Already in Homer’s Iliad—in the famous Catalogue of Ships—Onchestos is referred to as Poseidon’s “bright grove.” In the sixth-century Homeric Hymn to Apollo, the titular god is said to have sojourned at his uncle’s sacred grove on his way to found his own sanctuary at Delphi. According to the Hymn to Hermes, Apollo would pass again through this “lovely grove and sacred place of the loud-roaring Holder of the Earth [Poseidon]” in pursuit of his baby brother, Hermes, who had stolen his cattle. Other stories speak of an eponymous hero, one Onchestos, son of Athamas, who founded the sanctuary, as well as an early association with the royal house of Orchomenos, the powerful Mycenaean center situated to the sanctuary’s northwest. It was near Onchestos, at the Teneric plain, where Herakles fought Orchomenian troops who were advancing toward Haliartos, the city directly to the sanctuary’s west.

Archaeological evidence attests to the sanctuary’s prosperity in the sixth and fifth centuries BCE. Throughout this time, it was probably under the control of Thebes, one of the most prominent cities in the ancient region of Boeotia and located to the east of the sanctuary. A major religious festival, complemented by athletic competitions, was already being held at the sanctuary in the sixth century BCE. The fifth-century poet Pindar refers to the “celebrated victories with swift-footed horses” during these competitions. In the second half of the fourth century, the sanctuary became the religious center of the Boeotian Confederation (Koinon). After the destruction of Thebes in 335 BCE, if not earlier, the cult site came under the control of Haliartos. Architectural remains attest to an expansion of the sanctuary grounds. Among the archaeological evidence are proxeny decrees that reveal the bestowment of ambassador duties upon certain individuals and small bronze and lead tokens that were evidently used for the casting of votes.

Onchestos’ fortunes changed, however, as the Romans extended their hold over mainland Greece. The sanctuary was probably sacked alongside Haliartos in 171 BCE when the city sided with Rome’s opponents in the Third Macedonian War. Archaeological evidence suggests that the sanctuary might have continued to function in some capacity long after the Roman conquest of Greece in 146 BCE and the subsequent dissolution of the Boeotian League. Literary sources, on the other hand, provide contradictory information about the state of the sanctuary: the Greek geographer and historian Strabo, writing in the early first century CE, claims that Poseidon’s sacred grove was “devoid of trees” although the temple of Poseidon was standing. Meanwhile, over a century later, the Greek traveler Pausanias would write that he was able to see Poseidon’s temple, cult image, and grove. As for the late Roman and Byzantine eras (third century CE onwards), the archaeological record attests so far only to agricultural activity on the site.