Hewn blocks from submerged ruins associated with the name Thronion are exposed during low, low tide along the northeastern shoreline of the fan delta which separates the Gulf of Euboea from the Maliakos Gulf, central Greece. Although the date of these ruins is not known, their submergence indicates that they predate the most recent marine transgression. Late Holocene sediments of the coastal plain adjacent to the ruins were studied using 34 auger cores drilled along two 1.3 and 1.1 km shore-normal sections. Cores were described in the field and sampled for sedimentologic and microfossil analyses. These analyses show that late Holocene transgressive marine and strandline units interfinger inland with deposits of a brackish water embayment. Subsequent progradation of the shoreline is marked by overlying slightly brackish to freshwater marsh sediments. A soil horizon developed on these marsh sediments defines a period of aerial exposure and land stability. Late Roman to Byzantine sherds (ca. 4th-13th century) within the buried soil and a high phosphate content suggest that this soil developed in association with human habitation. The buried soil may be the surface on which the now-submerged ruins were built.