and maintain the context of artifacts.
- interpret a plan view of an archaeological site
- locate the position of each excavation unit
- reconstruct the context of each artifact within the grid
- explain the importance of the grid system
Grid unit - a square area of the grid system that is labeled by the coordinates in one corner.
Plan view - a map looking down on a site.
Provenience - the precise location of an artifact or other archaeological feature based on its position in the grid and how far under the ground surface it is found.
Site datum - an arbitrary point established off-site that is used to establish the grid system. It has grid coordinates of (0,0).
Background:
Click on this picture for a larger version!
When a site is excavated or disturbed in any way, artifacts are removed from their original context. Once they are dug up they can never be put back exactly as they were found, so archaeologists must record their position on paper. One way to do this is to establish a grid system over a site. Before excavating, a datum point is established at an arbitrary location and labeled (0,0). From this point a grid of equal-sized squares, or units, is laid out over the site. The corners of each grid unit are labeled according to their distance north, south, east, or west from the site datum. The material excavated from each grid unit is kept separately from the material from other units. In this way, an artifact from one grid unit will have a different provenience than an artifact from another unit.
A grid allows archaeologists to reconstruct the location of the artifacts on a map, or plan view, of the site. If the place where each artifact was found can be seen in a plan view, some patterns of artifact distribution may appear. These patterns give archaeologists insights into what activities occurred in a certain part of the site. For instance, shown here is the plan view of a structure at Old Mobile. Notice that most of the brick was found in one area of the site. Archaeologists believe this may be near where the structure's fireplace was located.
Click on this picture for a larger map of Structure X!
Artist's reconstruction of a house at Old Mobile based on recent excavations (drawing by Professor Phillipe Oszuscik, University of South Alabama).
- If a concentration of nails indicates that a wooden wall was once present, how many walls of Structure X have been uncovered so far? The location of iron nails in generally only three rows of the grid indicates that only three walls of the structure have been excavated. One corner of the building was probably in grid unit (1,2)
- What can we tell about the size of Structure X? The southernmost wall of the structure is the only one whose length is fully uncovered, but it can tell us about how wide the building was. According to the scale on the grid unit map, each side of a unit equals 1 meter, so Structure X was around 4 meters wide (about 13.5 feet).
- What could the concentration of window glass mean? The most likely answer is that a window was once located in the area where the pieces of glass were found.
- There are two large concentrations of artifacts. The one located outside the walls of Structure X doesn't include brick or fragments of copper kettle. What does this tell us about each of these groups of artifacts? The area of the site that has brick and pieces of copper kettle in addition to animal bone and pottery was probably the location of a fireplace. Found together, these artifacts tell us that cooking activity was taking place here. The concentration of artifacts located outside the structure probably represents a trash pit.