The coastal plain of the Pamisos River and five associated rivers at the head of the Gulf of Messenia in the southwestern Peloponnese includes middle through upper Holocene sedimentary-environment lithosomes of alluvial flood-plain deposits, channel sand, braided streams and deltas, bank swamps and marshes, dune fields, minor lagoons, beach-accretion ridges, and shallow-marine sediment. The areal distribution of these environments is in balance between the sediment supplied by the alluvial systems and their modification by coastal wave action. Questions remain about the importance of tectonic uplift and downwarp relative to sediment input and changes in eustatic sea level. Radiocarbon and pottery dates, drill cores, outcrops, and environmental studies have provided information for the development of a synthesis of paleogeographic change and its relationship to archaeological remains from the Neolithic period (middle Holocene) to the present. Examples include (1) a marine embayment extended into the area of the present Pamisos River flood plain near the town of Messini in middle late Holocene (Neolithic-Helladic) time, (2) rounded hills flanking the low-lying Karya River coastal plain were wave-cut cliffs in pre-Roman time, (3) the lower Karya River valley, now occupied by a braided stream, was a swampy lagoonal area, (4) major Early Helladic buildings at Akovitika were constructed along a shoreline, whereas the site is now surrounded by backswamp, and (5) the post-Roman delta–coastal plain of the Tsana River is now undergoing intense erosion. These types of paleogeographic analyses may prove of use to archaeologists in understanding the reasons for selection of habitation sites. They may also assist the modern occupants of the coastal area in coastal planning and in understanding rates and nature of coastal change at the head of the Messenian embayment.