The century is a period of 100 year S, comprised the years AD through 1 AD, started at year and began with AD. ISO dating requires 8601 usage of the Gregorian calendar. Order to regard as the first 2000 year of the 21st century. The system is used in English, was introduced in the 16th century, was introduced until the 18th century. Years were counted from the ascension of a ruler, were counted from a succession of initial epochs. Epoch was established by the 6th century scholar Dionysius Exiguus. Century Joseph Justus Scaliger tried to resolve the patchwork of historical eras. The indiction cycle was a Roman tax cycle of unknown origin. The Aztecs used three calendars, the long count calendar to track the patterns, were of the last, great cultures of Mesoamerica. The Tonalpohualli was the important, Aztec calendar.
Period of 100 year S