Contexts and Units
On my first day in the field at Khao Tao Chong I was one of the first students to start excavation, along with my partner Kyaw from Burma. The reason I find this day so important is because it was the first day of learning how to excavate a site.
Our excavation and recording method follows the single context recording system. You can read more about this in the Museum of London Archaeology Service Excavation Manual.
Context is important to an archaeologist because it refers to any discrete entity in a site, most of the time in our site it refers to discrete deposits of sediment that we can distinguish by colour, texture and consistency. Sometimes a context is very small and we excavate it all at once. Other times the context is quite big and thick and we excavate it several excavation units. We do this to keep artefacts from similar spaces and time periods together and prevent mixing artefacts from different events and locations in the site.
We follow the convention that many archaeologists have of using a one metre square as the smallest area of our excavation unit. In each square we excavate layers of 50 mm thick, or less if we encounter a change in context before we get to 50 mm. We expect that all artefacts and object found in an excavation unit are roughly the same age. This is a widely-held view amongst archaeologists and is called the ‘principle (or law) of association’ . Keeping together artefacts from the same period allows us to compare how human behaviour and the local environment changed in different time periods.
A related concept that we use is known as the law of superposition. This law states that all artefatcs on the upper units are younger than those in the lower units. It is very important for us as archaeologists to follow these rules when we try to make sense of how the site was formed and how human behaviours, as they are represented by the artefacts we find, changed over time.