An indiction is any of the years in a 15-year cycle used to date medieval documents throughout Europe, both East and West. Each year of a cycle was numbered: first indiction, second indiction, etc. However, the cycles were not numbered, thus other information is needed to identify the specific year.
When the term began to be used, it referred only to the full cycle, and individual years were referred to as being Year 1 of the indiction, Year 2 of the indiction, etc. But usage changed, and it gradually became common to talk of the 1st indiction, the 2nd indiction, and so on.
Indictions originally referred to the periodic reassessment for an agricultural or land tax in late third-century Roman Egypt. These were originally in 5-year cycles beginning in 287 AD, then in a non-cyclic series which reached number 26 by 318 AD. But by 314 AD, the 15-year cycle had appeared. The Chronicon Paschale (c. 630 AD) assigned its first year to 312–313 AD, whereas a Coptic document of 933 AD assigned its first year to 297–298 AD, one cycle earlier. Both of these were years of the Alexandrian calendar whose first day was Thoth 1 on August 29 in years preceding common Julian years and August 30 in years preceding leap years, hence each straddled two Julian years.
The indiction was first used to date documents unrelated to tax collection in the mid-fourth century. By the late fourth century it was being used to date documents throughout the Mediterranean. In the Eastern Roman Empire outside of Egypt, the first day of its year was September 23, the birthday of Augustus. During the last half of the fifth century, probably 462 AD, this shifted to September 1, where it remained throughout the rest of the Byzantine Empire. In 537 AD, Justinian decreed that all dates must include the indiction via Novella 47, which eventually caused the Byzantine year to begin on September 1. But in the western Mediterranean, its first day was September 24 according to Bede, or the following December 25 or January 1, called the papal indiction. An indictio Senensis beginning September 8 is sometimes mentioned.
The indiction for a modern Anno Domini year Y (January 1 to December 31) is
- (Y + 2) mod 15 + 1
For example, the indiction for the year 2011 is 4
- (2011 + 2) mod 15 + 1 = 4
So 2008, three years earlier, was a first indiction
- (2008 + 2) mod 15 + 1 = 1
This applies even when the Anno Domini year begins during the preceding September, as it did during the early Middle Ages.
The indiction for a Byzantine AM year (beginning September 1) is found by dividing that year number by 15 and taking the remainder (modulus). If the remainder is zero, then the indiction is 15. For example, the Byzantine year AM 6961, when Constantinople fell to the Ottoman Turks, is indiction 1
- 6961 mod 15 = 1
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- Yiannis E. Meimaris, Chronological systems in Roman-Byzantine Palestine and Arabia (Athens, 1992), 32-34
- Chronicon paschale 284–628 AD, trans. Michael Whitby, Mary Whitby (Liverpool, 1989), 10.
- Depuydt, Leo (1987). "AD 297 as the beginning of the first indiction cycle". The bulletin of the American Society of Papyrologists. 24: 137–9.
- Roger S. Bagnall, K. A. Worp, The chronological systems of Byzantine Egypt (Zutphen, 1978).
- Bonnie Blackburn, Leofranc Holford-Strevens, The Oxford companion to the year (Oxford, 1999), 769-71.
- V[enance] Grumel, "Indiction", New Catholic encyclopedia.
- S. P. Scott [Justinian I], "Forty-seventh new constitution" [Novella 47], The civil law [Corpvs jvris civilis] (1932; reprinted New York, 1973), 16 (in 7): 213-15.
- Dates and dating
- A chart of years and their indictions