1 Relative Chronology and Archaeological Sequencing

What relative chronology establishes

Relative chronology arranges deposits, artifacts, and events as earlier than, later than, or contemporary with one another. It establishes sequence, not a calendar date or the amount of time between events. Archaeologists build these sequences by combining stratigraphic relationships with comparisons among artifacts, assemblages, and sites.

Reading stratigraphic relationships

Stratigraphy examines the layers, or contexts, formed by deposition and other events at a site. In an undisturbed sequence, the principle of superposition holds that a lower deposit was generally laid down before the deposit above it. This basic older-to-younger ordering is valid only when the layer relationships have been correctly identified and later disturbance has been considered.

A cut, such as a pit, trench, or grave, interrupts earlier deposits. Its fill was deposited after the layers it cuts. If a pit cuts layer A and is filled with layer B, layer A predates the cut and its fill; the fill may then be overlain by later deposits. Recording such relationships helps reconstruct events including deposition, construction, use, cutting, and abandonment.

A Harris matrix diagrams relationships among individual contexts, linking them in a sequence. It helps organize complex excavations and show which contexts are securely ordered, but it does not assign dates in years.

For example, a natural soil is covered by a house floor, a posthole cuts the floor, and a later layer seals both. The order is natural soil, then floor, then posthole cut and fill, then sealing layer. This establishes order, not the number of years between events.

Disturbance and context integrity

Stratigraphic order can mislead if site formation is not taken into account. Burrowing animals, roots, construction, erosion, ploughing, and later excavation can mix or move materials. A layer can contain residual objects, which are older artifacts redeposited in a later context, or intrusive objects, which entered an older layer from above.

An artifact’s position is evidence about its context, but does not automatically guarantee when the artifact was made or deposited. Archaeologists assess the integrity of contexts and the relationships among them before drawing chronological conclusions.

Comparing artifacts through time

Typology groups artifacts by recurring attributes such as shape, manufacturing technique, or decoration. If styles and technologies changed through time, similarities and differences among types can help establish a relative sequence. Typology is most useful when classifications rely on clearly described features and the sequence is supported by independent evidence, such as stratified finds.

Seriation arranges artifacts or assemblages into a relative order based on patterns of change. In frequency seriation, the proportions of several pottery styles are compared across contexts. A style that rises in frequency and later declines can produce a distinctive pattern that helps order assemblages.

Seriation depends on assumptions about how styles spread and changed. Patterns can be distorted if objects were used for a long time, traded between communities, or differed between regions. A typological or seriated sequence does not necessarily reveal a precise date, the duration of a style, or the exact order of every individual artifact. Its strength depends on the quality and context of the evidence.

Linking contexts and sites

Cross-dating uses an object or pattern whose relative position is known in one context to help order a context elsewhere. For example, a distinctive pottery type found in a securely ordered sequence at one site can provide a basis for comparison when it also appears at another site.

The inference is strongest when the type is well identified, the contexts are reliable, and the type’s movement or persistence between places is understood. Cross-dating links one sequence to another; without an independently dated anchor, it does not provide a calendar date.

Other comparisons may use associated fossils, distinctive volcanic ash layers, or historically documented objects. These can help place deposits in relation to one another, but association must be evaluated carefully. Materials found near one another were not necessarily deposited at the same time, particularly where mixing or redeposition occurred.

Combining evidence and recognizing limits

A sound relative chronology draws on several lines of evidence. Stratigraphy can order contexts at a site, typology and seriation can compare artifacts among contexts, and cross-dating can link sequences between sites. Agreement among methods increases confidence in the ordering. If methods conflict, archaeologists revisit context integrity, artifact identification, and the assumptions behind each comparison.

Relative chronology alone cannot establish how many years ago an event occurred, how long an occupation lasted, or whether events in different places happened at the same time. Radiocarbon dating is a different, numerical method that can estimate the age of suitable once-living material. Relative methods help place a radiocarbon sample and its context in the site sequence, but the result dates the sampled material, not automatically every associated artifact or event. Interpretation depends on the sample selected and its archaeological context.