An indiction is any of the years in a 15-year cycle used to date medieval documents throughout Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, 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
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...

. These were originally in 5-year cycles beginning in 287, then in a non-cyclic series which reached number 26 by 318. But by 314 the 15-year cycle had appeared. The Chronicon Paschale
Chronicon Paschale
Chronicon Paschale is the conventional name of a 7th-century Greek Christian chronicle of the world...

(c. 630) assigned its first year to 312–313, whereas a Coptic
Coptic Christianity
The Coptic Orthodox Church of Alexandria is the official name for the largest Christian church in Egypt and the Middle East. The Church belongs to the Oriental Orthodox family of churches, which has been a distinct church body since the Council of Chalcedon in AD 451, when it took a different...

 document of 933 assigned its first year to 297–298, 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
Julian calendar
The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...

 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
Augustus ;23 September 63 BC – 19 August AD 14) is considered the first emperor of the Roman Empire, which he ruled alone from 27 BC until his death in 14 AD.The dates of his rule are contemporary dates; Augustus lived under two calendars, the Roman Republican until 45 BC, and the Julian...

. During the last half of the fifth century, probably 462, this shifted to September 1, where it remained throughout the rest of the Byzantine Empire
Byzantine Empire
The Byzantine Empire was the Eastern Roman Empire during the periods of Late Antiquity and the Middle Ages, centred on the capital of Constantinople. Known simply as the Roman Empire or Romania to its inhabitants and neighbours, the Empire was the direct continuation of the Ancient Roman State...

. In 537 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
Bede , also referred to as Saint Bede or the Venerable Bede , was a monk at the Northumbrian monastery of Saint Peter at Monkwearmouth, today part of Sunderland, England, and of its companion monastery, Saint Paul's, in modern Jarrow , both in the Kingdom of Northumbria...

, or the following or , called the papal indiction. An indictio Senensis beginning is sometimes mentioned.

The 7980-year Julian Period was formed by multiplying the 15-year indiction cycle, the 28-year solar cycle
Solar cycle (calendar)
The solar cycle is a 28-year cycle of the Julian calendar with respect to the week. It occurs because leap years occur every 4 years and there are 7 possible days to start a leap year, making a 28 year sequence....

 and the 19-year Metonic cycle
Metonic cycle
In astronomy and calendar studies, the Metonic cycle or Enneadecaeteris is a period of very close to 19 years which is remarkable for being very nearly a common multiple of the solar year and the synodic month...


The indiction for a modern Anno Domini
Anno Domini
and Before Christ are designations used to label or number years used with the Julian and Gregorian calendars....

 year Y (January 1 to December 31) is mod
Modular arithmetic
In mathematics, modular arithmetic is a system of arithmetic for integers, where numbers "wrap around" after they reach a certain value—the modulus....

 15 + 1
For example, the indiction for the year 2011 is 4 mod 15 + 1 = 4
So 2008, three years earlier, was a first indiction 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
Byzantine calendar
The Byzantine calendar, also "Creation Era of Constantinople," or "Era of the World" was the calendar used by the Eastern Orthodox Church from c. 691 to 1728 in the Ecumenical Patriarchate. It was also the official calendar of the Byzantine Empire from 988 to 1453, and in Russia from c...

 (beginning September 1) is found by dividing that year number by 15 and taking the remainder (modulus
Modular arithmetic
In mathematics, modular arithmetic is a system of arithmetic for integers, where numbers "wrap around" after they reach a certain value—the modulus....

). If the remainder is zero, then the indiction is 15. For example, the Byzantine year AM 6961, when Constantinople
Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

 fell to the Ottoman Turks
Ottoman Turks
The Ottoman Turks were the Turkish-speaking population of the Ottoman Empire who formed the base of the state's military and ruling classes. Reliable information about the early history of Ottoman Turks is scarce, but they take their Turkish name, Osmanlı , from the house of Osman I The Ottoman...

, is indiction 1
6961 mod 15 = 1
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