Phosphates, plowzones, and plazas: a minimally invasive approach to settlement structure of plowed village sites

Inferences about settlement structure play an important role in explanations of social and political change in Late Prehistoric eastern North America, but ethical and logistical challenges posed by extensive horizontal excavations mean that archaeologists must develop low cost, minimally invasive methods for investigating key properties of village structure. There are two important components of most villages in the region: 1) the peripheral distribution of middens; and 2) the size and location of formal communal spaces or plazas, each of which leaves traces in soil chemistry. In shallowly buried, plowed village sites where artifacts have been physically displaced, the chemical signature of middens may be more resistant to disturbance and provide an enduring signature of ancient settlement structure. We conducted a systematic soil phosphorus survey at the Reinhardt Site (33PI880) in central Ohio, the primary occupation of which occurred during the Late Prehistoric Period (ca. AD 1200–1450), to test for the presence and approximate size of a central plaza and the shape and distribution of peripheral midden deposits. Soil samples from the modern plowzone (N = 131) were analyzed for Mehlich II extractable phosphorus using molybdate colorimetry. The interpolated phosphorus distributions indicate a clear ring midden approximately 90 m across with an internal plaza that is roughly 30 m × 40 m. Artifact distributions from a shovel test pit survey and interpolations of plowzone magnetic susceptibility measurements identify the location of the village but are ambiguous with regards to village size and do not clearly distinguish the central plaza. Our results suggest that systematic surveys of soil phosphorus are a rapid, minimally invasive, and inexpensive method for generating data on the size and shape of villages and their plazas.

► We compare phosphates, magnetic susceptibility, and artifacts from a plowed village.
► All three methods identified the village location.
►  Only phosphate analysis distinguished a 30 m+ diameter central plaza.
► Phosphate survey is a rapid, minimally invasive method to identify plaza size in plowed fields.