The question of the dates of the objects and events discovered through archaeology is the prime concern of any system of thought that seeks to summarize history through the formulation of ages or epochs. An age is defined through comparison of contemporaneous events. Increasingly, the terminology of archaeology is parallel to that of historical method. An event is "undocumented" until it turns up in the archaeological record. Fossils and artifacts are "documents" of the epochs hypothesized. The correction of dating errors is therefore a major concern.