The tell of Kirrha is the largest prehistoric site (Middle to Late Helladic I) in Phocis (Greece), covering an area of around 6 hectares. Located downstream of the deltaic plain of Delphi and close to the present-day coastline, its deepest, and therefore oldest, archaeological levels have never been reached. The following article discusses the results of the geoarchaeological investigation of the tell. Information about the internal structure of the tell was gathered for the first time through ARP and ERT geophysical surveys, two core drillings, some sedimentological analyses and radiocarbon dating. The date of its earliest occupation could also be obtained. The results indicate a thickness of occupation layers ranging from 9 to 11 meters (until 2 m b.s.l.). While some archaeological indicators found in the cores (such as very isolated pottery fragments) suggest a probable Neolithic occupation, the radiocarbon dating results presented here indicate a first occupation at the very beginning of the Bronze Age (Early Helladic II). Palaeoenvironmental reconstruction reveals that the first inhabitants of Kirrha settled in a coastal-marsh-type environment that was being filled in by fine-grained alluvial deposits from the Pleistos and Hylaithos rivers. Geophysical surveys also revealed that parts of the tell have been eroded by a palaeochannel or buried under alluvial sediments.