Archaeological remains traditionally are defined in terms of time, space, and style. Without absolute dating, style was useful for defining related archaeological materials, but positioning defined units of style in time often proved problematic. Concerns over chronology dominated much early archaeological work in various parts of the world (5⇓–7), especially because often it was difficult to relate spatially separated archaeological remains to each other. Although stratigraphy and seriation could be used to provide relative dating for past remains, cross-dating between sites was challenging.