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. However, the cycles were not numbered, thus other information is needed to identify the specific year.
History
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 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 reason for beginning the year at that time was that the harvest would be in, and so it was an appropriate moment to calculate the taxes that should be paid. 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, which eventually caused the Byzantine year to begin on. But in the western Mediterranean, its first day was according to Bede, or the following or, called the papal indiction. An indictio Senensis beginning is sometimes mentioned. The 7,980-year Julian Period was formed by multiplying the 15-year indiction cycle, the 28-year solar cycle and the 19-year Metonic cycle.
Terminology
When the term "indiction" 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. It gradually became common to apply the term to the years themselves, which thus became the first indiction, the second indiction, and so on.
Calculation
The indiction for a modern Anno Domini year Y is For example, the indiction for the year 2011 is 4 So 2008, three years earlier, was a first indiction 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 is found by dividing that year number by 15 and taking the remainder. 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
