The science of chronology, as it applies to the Middle Ages, treats of the method of reckoning time by year or era. This article discusses the subject in its Christian orientation as it applies to the East and to the West.
THE CHRISTIAN EAST
In addition to Olympiads, regnal years, consulates, and other civil and political eras that continued to be used as chronological indexes, the Christian East had its own methods of determining chronology, viz, according to world eras, and cycles.
World eras. These were formed on the basis of three factors: (1) the idea that the world would last 6 millenniums, corresponding to the 6 days of Genesis, the coming of Christ occurring in the middle of the 6th millennium;(2) the need to find a Friday coinciding with the paschal moon as a date for the Passion; (3) the belief that the paschal cycles of the moon must have a proleptic connection with Creation. Hence arose the various cycles and the various eras.
The Lunar Cycle of Anatolius and the World Era of Julius Africanus. anatolius of Laodicea established a 19-year lunar cycle, constructed on the new moon (neomenia ) of the vernal equinox (March 22), beginning in 258, equivalent in the world era of julius Africanus –5501 (the minus signs indicates years before the birth of Christ) to 5759. By taking into account the precyclic year, which supposed 11 epacts from its beginning, the cycle through complete revolutions (303 x 19) rejoins the first year of the world era. In addition, the chronology of the Passion according to Africanus, 13 lunae, March 23 through 31, is in agreement with the cycle of Anatolius for that same year (2d of the cycle).
The World Era of Alexandria. When the Alexandrines moved the equinox back to March 21, they changed the cycle by constructing it on the new moon of the first of the year (Thoth 1 = August 29). The inaugural year, 304, the 9th year of the cycle of Anatolius, was eight years later than his. In the 5th century, Panodorus adapted a world era to this cycle: –5493, placing the Incarnation in 5494 (= 1) and the Passion in 5526 (–34). Annianos, his rival lowered it to –5492, fixing the Incarnation at March 25, 5501, and the Resurrection at March 25, 5534 (= 42), March 25 also being the day of Creation. This Alexandrine era was favored by ecclesiastical writers. Its year began on March 25, sometimes on September 1 on the occasion of the indiction.
Protobyzantine Era. Constantinople reformed its computation in 353 by adjusting the cycle according to the equinoctial neomenia, March 21. Accordingly, with the addition of the precyclic year, this cycle began nine years earlier than that of Anatolius. The latter was to have begun again in 353. The new cycle, therefore, had its beginning in 344. The world era that followed was eight years earlier than that of Africanus, therefore, –5509. The birth of Christ was placed at 5507 (= –3) and the Passion at 5540 (= 31). The year began March 21.
Byzantine Era. This was constructed by subtracting a year from the cycle and from the protobyzantine era to make these agree with the indiction. The era was therefore –5508. It made its first appearance in 630 with the computist Georgios, who nevertheless retained the Alexandrine chronology for Christ. This latter was finally abandoned and the Passion reestablished at the year 91 (5539 of the era). The year had its beginning on September 1.
Other World Eras. The Era of Malalas: –5565; birth of Christ: 5967 (= –2); Passion: 6000 (= 31). The Era of Abdisho (Nestorian): –5491; birth of Christ: 5490 (=–2). The Georgian Era: –5604, constructed on the basis of the protobyzantine cycle of 344.
Particular eras. Era of Diocletian: 284, Thoth 1 (August 29). The years of the reign of this emperor, first used to date Easter, were later used to fix the dates of documents and events. The Armenian Era (undetermined years)–July 11, 522; the Little Armenian Era (fixed years)–starting point, Aug. 11, 1084. The Era of the Ascension (used by John Malalas and the Chronicon paschale, as well as by the Nestorian Syrians): beginning date, the year 31.
Cycles. (1) Lunar cycles (19 years) and solar cycles (28 years), were used in synchronism. It is well to note whether the Alexandrine or Byzantine cycle is employed (see table in Grumel, 266–267). (2) Paschal cycles of 532 years, product of 10 x 28 (see Grumel): (a ) The Georgian paschal cycle (532 years) was called protobyzantine cycle of 344. (b ) The Ethiopian paschal cycle was called the years of Mercy or of Grace—it began with the era of Diocletian, Aug. 19, 284. (3) indictions, which were periods of 15 years.
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