The establishment of the temporal sequence of prehistoric events. During the nineteenth and early twentieth centuries archeologists devised a number of methods to construct a relative chronology for cultural remains. These included stratigraphy (correlation of layered sediments and rocks), seriation (ordering of materials based on changes in style), and cross-dating (using temporally diagnostic ceramic and stone tool types). Beginning in the early twentieth century, dating methods developed in the natural sciences began to be applied to archeological remains to provide absolute (that is, calendar) dates. These are sometimes called chronometric dating methods, and the more commonly used ones are described here.