The Ground Is an Archive
Every occupied place accumulates: floors are laid, walls collapse, pits are dug and refilled, dust settles. Archaeology's founding insight, borrowed from geology, is that this accumulation has rules — and the rules turn dirt into a dated document.
| Principle | Statement | Consequence |
|---|---|---|
| Superposition | In undisturbed deposits, lower layers are older | Depth is a relative clock |
| Cutting | A cut (pit, ditch, grave) is younger than everything it cuts | Intrusions date after their targets |
| Filling | A fill is younger than the cut that contains it | Pit contents postdate the pit |
| Association | Objects sealed in one context entered the ground together | The context, not the object, is the dating unit |
The recording unit is the context: a single depositional event — one layer, one cut, one fill. A site is thousands of contexts, and the Harris matrix (Edward Harris, 1973) diagrams their complete older/younger relationships as a flowchart of time — the site's stratigraphy with the soil removed.
The Two Termini
A dated object inside a layer brackets the layer's age from one side only:
- Terminus post quem (TPQ) — "limit after which": a coin struck in 120 CE inside a fill means the fill closed no earlier than 120. It could be centuries later — coins circulate and linger.
- Terminus ante quem (TAQ) — "limit before which": a structure sealed beneath the datable layer must be older than it.
The classic trap — residuality: old things end up in young layers constantly (a Roman coin in a medieval pit is unremarkable). The reverse — a young thing in a truly sealed old layer — is impossible. That asymmetry is why one anachronistic sherd can redate an entire deposit later, but a thousand old sherds cannot push it earlier. The latest object in a context sets its TPQ.
Relative dating orders events without calendar years; the next lesson's laboratory methods pin the order to numbers. The order comes first — a radiocarbon date from a misread context dates the wrong event precisely.
Watching Time Deposit Itself
The animation builds a site the way time did: floor, occupation debris, collapse, windblown soil — layer on layer. Then a pit knifes down through three of them and refills. Watch the section drawing acquire its logic: the pit's cut line truncates every layer it passes through, so the pit must be younger than all of them, no matter how deep its bottom reaches.
Finally the layers lift out of the ground one by one and rearrange into the Harris matrix — boxes and lines, oldest at the bottom, the pit branching in at its true position. The section shows where things are; the matrix shows when. Depth was never the clock — sequence is, and the pit that reaches deepest while dating youngest is the proof.