Investigations in the Cahokia Site Grand Plaza

Abstract

Research designed to explore the Grand Plaza at the Cahokia Mounds site, the largest Mississippian-period mound center in the eastern United States, documents that plazas may yield significant information regarding Mississippian manipulation of the landscape and the initial growth of mound centers. Probing and excavation within the Grand Plaza revealed that buried ridge-swale topography, identified through an electromagnetic-conductivity survey, was stripped and then filled by the Cahokians. Excavation also corroborated the presence of deep-pit borrows identified by remote sensing. Based on the ceramics recovered from our excavations, we argue that these earth-moving events were initiated prior to the onset of the Mississippian period (ca. A.D. 1000). Reclamation of the borrowed areas resulted in the formation of the mound-plaza configuration early during the Mississippian period.

Solving archaeological problems using techniques of soil magnetism

“…The large lateral borrow, however, was not apparent (Dalan, 1991); fill soils used in reclaiming this area are too similar to the clayey swale soils naturally occurring in this location. Only through magnetic measurements, supplemented by soil-morphological examinations (conducted as part of test excavation [Holley et al, 1993]) and soil-chemical studies (e.g., determinations of whole-soil texture, organic carbon, pH, and total phosphorus) were we able to identify and define this feature.…”

“…Later fills contain less midden debris and are quite homogenous; this upper layer of fill was placed to elevate the area to create a clean and level plaza surface. Dating of ceramics recovered from the fill by test excavations has provided critical evidence for the initiation of significant landscape-modifying activities late within the Emergent Mississippian period (A.D. 800-1000) as well as for the early formation of a site center that included not only a principal mound (i.e., Monks Mound) (Reed et al, 1968;Fowler, 1989), but also a Grand Plaza complex (Holley et al, 1993;Dalan, 1997). Subsequently, a portion of this lateral borrow was reexcavated to obtain sediments for the construction of a mound (Mound 49).…”

Flood management along the Lower Mississippi and Rhine Rivers (The Netherlands) and the continuum of geomorphic adjustment

“…Extensive and prolonged human occupation occurred along the Mississippi Valley in sites such as Cahokia, the largest prehistoric earthen mound in North America (Holley et al, 1993). Many large prehistoric population centers contributed to extensive floodplain earth works, such as mounds and terraces, and floodplain borrow pits have been documented from Fig.…”

Geophysical indicators of culturally emplaced soils and sediments

“…As an example, let us return to the Cahokia Mounds Site and examine the case of a "negative" earthen feature: the Grand Plaza at the center of this community (Holley et al, 1993). Electromagnetic conductivity surveys over this level surface documented buried ridge and swale topography relating to ancient movements of the Mississippi River as well as several small reclaimed borrow pits located adjacent to mounds positioned around the plaza.…”