The Law of Superposition. In an undisturbed sequence, the oldest layer is at the bottom and each layer above it is younger. Borrowed from geology and applied to human deposits, this is the foundation the whole discipline rests on. Note the qualifier: undisturbed. Almost the entire skill of excavation lies in spotting where that condition fails.

Why cuts change everything. A pit, ditch, grave or posthole is not a layer — it is a removal. It is necessarily younger than every deposit it passes through, and its fill is younger still. Get a cut wrong and you can date a site by an object that arrived a thousand years after the layer it appears to sit in. Intrusive finds are one of the commonest sources of bad archaeological dates.

The Harris matrix. Developed in 1973 in Winchester, England, by Edward C. Harris, it depicts the temporal succession of archaeological contexts as a diagram. It was devised to overcome the limits of conventional section drawings: a section shows only what a single vertical slice happens to intersect, while the matrix translates the three-dimensional arrangement of deposits into a two-dimensional graph carrying a fourth dimension — time. It became standard practice remarkably fast, because it forces the excavator to state relationships explicitly rather than leaving them implied in a drawing.

Context is the unit. Modern excavation records the context — one depositional or destructive event — as its basic unit, not arbitrary depths. This was a real methodological shift: digging in fixed spits produces tidy sections and scrambled evidence. Recording by context is slower and it is the only method that preserves the sequence.

Relative, not absolute. Stratigraphy tells you order, never calendar dates. "Layer 4 is older than layer 3" is all it gives you. Absolute dates come from elsewhere — radiocarbon, dendrochronology, coins, datable pottery — and are then hung on the stratigraphic framework. The sequence is the skeleton; the dating methods are the flesh. Getting the skeleton wrong makes every date attached to it wrong too.

Excavation destroys its own evidence. Unlike almost any other science, the experiment cannot be repeated: digging a site removes it permanently. The record — context sheets, drawings, photographs, the matrix — becomes the site. That is why the paperwork in step 8 is not bureaucracy. It is the only thing that will survive.

Excavation

Blueprints (2)

Excavation Grid and Context Sheet

Reading Stratigraphy