**The archaeologist works tirelessly** to place material evidence from the past within a chronological framework. Every object—whether a wall, mosaic, piece of pottery, coin, ditch, temple, house or inscription—must undergo a critical examination aimed at establishing what it is by describing its immediately observable physical and morphological characteristics, in the hope that these bear a definite relationship to time. Furthermore, all information about its surroundings must be collected: location, depositional context and association with other objects. Once these conditions have been met, a chronological framework may conceivably claim a degree of validity for the time being, pending further data.
"Relative" and "absolute" chronologies
=============================================================================================================================================
However inappropriate they may be, the terms relative chronology and absolute chronology nevertheless describe two equally valid ways of situating evidence in time. The former comes almost naturally to archaeologists, especially those with few or no written sources, such as prehistorians and protohistorians. In this sense, related objects, such as pottery or archaeological layers, are ordered so as to reveal which come before, after, or at the same time as one another. This is why the chronology is called "relative." Three tried-and-tested methods can establish such relationships: seriation, stratigraphy and spatial analysis.
"Absolute" chronology seeks to place material evidence on a calendar timescale. For schoolchildren, this is the time shown by the timeline running around the classroom walls: linear and calculable. A few rare archaeological objects, such as coins or stone inscriptions, can be read in ways that provide relatively easy access to a date—or, more accurately, a range of possible dates. In everyday understanding, however, absolute chronology is most readily associated with methods based on physical laboratory measurements, whether obtained through radiocarbon dating, archaeomagnetism or thermoluminescence.
Bayesian statistics (see the preceding pages) can help reconcile these two approaches. Unlike classical frequentist statistics, it can readily take account of information associated with the context of events as well as dating measurements. Such information—including temporal ordering relationships inferred from the position of one event relative to another—is incorporated via the Bayesian model's prior distribution. This technique is particularly valuable when the material culture of the civilizations under study contains no artifacts suitable for dating whatsoever. Faced with this gap, one might be tempted to seek parallels with neighboring civilizations whose chronology is better established because they have more complete sources, or simply to rely on a traditional dating scheme. In either case, the proposed chronologies would rest on fragile foundations far removed from the discovery's actual context.
