Helike is a unique case of a classical Greek city (polis) that was destroyed, submerged, remembered in literary sources, but whose physical remains were lost and only recently located through combined geological, geoarchaeological, geomorphological, and archaeological methods. Its patron deity was Poseidon Helikonios; the sanctuary of Poseidon was pan-Hellenic in reputation. The region where Helike stood is seismically active. The catastrophe in 373 BCE destroyed the city at night, and according to ancient authors the sea rushed in after an earthquake, submerging the city.

Over subsequent centuries, visible ruins were reported; later the site silted over and became hidden under alluvial and marine sediment. In modern times work to locate it has involved borehole drilling, geophysical surveys, magnetometry, etc. The site has yielded traces of occupation spanning from the Early Bronze Age through Mycenaean times (Late Bronze period), through Geometric, Classical, Hellenistic, Roman, into Byzantine periods.

circa 1600–1400 BCE

Early Bronze Age Period
Helike (or proto-Helike) was occupied in the Early Bronze Age (circa 3000-2000 BCE / Early Helladic), during the Early Helladic periods (Early Helladic II-III, mid- to late third millennium BCE). In the modern village of Rizomylos, a coastal EH settlement was discovered. This settlement had large rectilinear buildings, cobbled streets, corridor houses; architectural forms and rich pottery assemblages with luxury items in gold and silver. The settlement appears well organized, with standardized manufacturing of storage jars, burnished and painted pottery, etc. In the Iliad, the famous Greek poet Homer states that the city of Helike participated in the Trojan War as a part of Agamemnon's forces. However, after flourishing it appears to have been abandoned at some point, and many of its contents were sealed under thick clay deposits.

Late Bronze Age / Mycenaean Period
Evidence shows a Mycenaean occupation near the Helike plain during this period (circa 1600-1100 BCE / Late Helladic), especially in the area of Nikolaiika, to the southeast of the Early Bronze Age site. Pottery from Late Helladic times, of fine quality, both painted and plain, has been recovered. Some domestic architecture or occupation-related features are evident. Thus Helike was part of the Mycenaean cultural sphere.

Geometric to Archaic Periods
After the collapse of the Mycenaean palatial system (circa 1100-479 BCE), Helike continued to be occupied. In the Geometric period (roughly 9th–8th centuries BCE), archaeological remains in Nikolaiika include walls and hearths, pottery typical of the period, drinking vessels (kantharoi etc.). The Archaic period saw growth in civic and religious institutions; the sanctuary of Poseidon Helikonios becomes prominent. Helike minted coins before its destruction, showing Poseidon’s head and symbols such as tridents and dolphins. The city led the twelve cities (Dodekapolis) of the Achaean League by Classical times.

Classical Period
This is the period (circa 479-323 BCE) of Helike’s greatest prominence in literary accounts. In 373 BCE, in a winter night, a violent earthquake struck, collapsing buildings, then a tsunami engulfed the city and submerged it. All inhabitants perished; according to sources, ten Spartan ships in its harbour were lost too. The area immediately beneath the city (coastal plain) sank; the site was thereafter submerged in water, then turned into a lagoon, and later partially land as sediments silted it in. Ancient authors like Strabo, Pausanias, Seneca, Diodorus etc wrote about ruins visible under water or just above water.

Post 373 BCE Periods
Though Helike as a functioning city ended in 373 BCE, its ruins remained visible and known. In Hellenistic and Roman times, travelers reported submerged walls and ruins under the water or in lagoon. Pausanias in the 2nd century CE notes submerged ruins, though damaged by salt water. Over time more sedimentation led to burial. Byzantine period records mention remains until the middle Byzantine times (9th-10th centuries CE). In later centuries the precise location was lost, though local memory and legend survived.

circa 1600–1400 BCE

The remains of Helike lie within the flat coastal plain of the Helike Delta, near the modern village of Rizomylos, a short distance from the Gulf of Corinth / Corinth. Today the site is situated several kilometres inland, buried beneath layers of lagoonal and fluvial sediments deposited over more than two millennia. Borehole studies and excavations have shown that the ruins are sealed at depths between three and five and a half metres below the modern surface, evidence of the geomorphological shifts caused by earthquakes, subsidence, and deltaic processes. The geology of the area is marked by the Helike Fault, which played a decisive role in both the catastrophe of 373 BCE and the preservation of the city’s archaeological record.

Archaeological research has revealed that Helike was not a single, static settlement but a landscape of successive occupations. In Rizomylos, excavations uncovered an Early Helladic period settlement characterized by rectilinear buildings, cobbled streets, and corridor houses, a type associated with complex social organization. The assemblage included luxury items in gold and silver alongside standardized ceramic production, pointing to both wealth and specialized craft activity. This early settlement was abruptly sealed by thick clay deposits, effectively preserving its contents.

To the southeast, at Nikolaiika, evidence of later occupation spans the Mycenaean and Geometric periods. Pottery of both decorated and plain varieties has been recovered, and domestic features such as walls and hearths attest to continuous habitation after the decline of the palatial centres. These finds demonstrate that the Helike plain remained integrated into the wider Aegean cultural networks from the Late Bronze Age through the early Iron Age.

The Classical city itself, destroyed in 373 BCE, has been identified in layers beneath lagoonal sediments at Rizomylos. Excavations have exposed collapse deposits consisting of cobblestones from fallen walls, roof tiles, and pottery of Classical date. This destruction horizon matches the historical accounts of the earthquake and tsunami that engulfed the city, offering rare archaeological confirmation of the literary tradition. In Valimitika, further west, later phases of occupation are represented by a substantial Hellenistic industrial complex, with basins (inspect), workshops, and storage areas, pointing to a reorganization of activity in the region after the demise of the classical Greek polis.

The broader landscape also preserves traces of later infrastructure, including a section of the Roman road that once linked ancient Corinth with Patras. Together, these remains illustrate a long and complex history of occupation, destruction, and reuse, layered within the sediments of the delta. The combination of Early Bronze Age urbanism, Mycenaean and Geometric domestic life, the sudden obliteration of a Classical polis, and later reoccupation provides a uniquely stratified picture of Achaean history, with the geology of the Helike Delta serving both as agent of destruction and as custodian of preservation.

circa 400 BCE

Poseidon Helikonios Coin
A bronze dichalkon from Helike in Achaia, Peloponnese, measuring 23 mm and weighing 2.98 grams. It dates to the early 4th century BCE, before the city’s destruction in 373 BCE. The obverse shows the diademed head of Poseidon Helikonios facing right, framed by a circular border resembling breaking waves, with the inscription “ΕΛΙΚ”. The reverse depicts a trident flanked by two dolphins swimming upwards, all enclosed within a laurel wreath tied at the bottom. This type is published in Lambros (p. 16, pl. 1, no. 15) and in Traité, no. 831.

Others
In the space of a possible little Poseidon temple, beginning around 850 BCE, religious artifacts like bronze and clay items such as figurines, clay chariot wheels, iron weapons, and pottery dating to the Archaic period, a bronze snake head and rare golden necklace were found.