From OrthodoxWiki:
Indiction
Indiction is a term given to identify an era or epoch of years of the calendar that was first used in the late third century to date agricultural and land tax cycles in Roman Egypt. By the late fifth century the indiction became widely used throughout the Mediterranean. Its use is still reflected in the Christian church calendars. The indiction in the Orthodox Church is on September 1.
Background
While the measure of a day and year have been labeled, and changed over the years, for time immemorial, the tagging of a period of years has varied throughout history. Eras or epochs of years have been measured from various starting points have been based on various events. These measures have included counts based upon the cycle of Olympiads, epochs starting from the founding of Rome, on the reigns of monarchs such as used today in Japan (the Meiji or Showa eras), from the formation of earth, and so on. In much of the world today the enumeration of years is based on the birth of Christ, although this practice, or epoch, did not become common for centuries after Dionysius Exiguus, a Scythian monk, established this starting point in 527.
In the third century in the Roman Empire an epoch measurement became popular called the Indiction. When indictions began to be used about 287, it originated as a cycle of five years. By 314 an indiction cycle of fifteen years appeared which became the common measure at the same time that the Emperor Constantine the Great recognized Christianity. The use of indictions for dating documents not related to taxes began in the mid-fourth century.
Each indiction itself was not distinctly identified, only the year within the indiction. Thus, an indiction may need reference to some other event to identify a specific indiction. Additionally, different systems of calculating the indictions came into use of which the following are most common:
In the eastern Roman Empire, in the Greek or Constantinopolitan Indictions the first day (of the new year) of the indiction year was established initially as September 23, which was the birthday of Augustus. This date also became the start of the Eastern Orthodox Church year. By late in the fifth century the start of the new year, however, shifted to September 1, which is the present day beginning of the Church year.
In the west, the Imperial or Western Indictions September 24 was adopted as the beginning of the year, apparently based upon calculations under the authority of the Venerable Bede.
Later, in the ninth century Roman or Pontifical Indictions were introduced in the west that began the year on either December 25 or January 1.
