#e <t>calendar<d>4004 Oct 23<n>Ussher's creation date<c>Mesopotamia<info>This is the date when Bishop James Ussher (in A.D. 1611) reckoned time began.
#e <t>calendar<d>3114 Aug 13<n>beginning of Mayan great cycle<c>Central America<info>August 13, 3114 B.C. is the zero date for the Mayan long-count calendar.
#e <t>calendar<d>432<n>Metonic cycle<c>Athens<info>The greek astronomer Meton discerned a 19-year period over which lunar phases repeat on nearly the same calendar dates.
#e <t>calendar<d>238<n>365.25-day year proposed<c>Alexandria<info>Ptolemy III ordered a 365.25-day calendar, but the quarter day is not accepted by the priest caste.
// Rome
#e <t>calendar<d>735<n>1 A.U.C.<c>Rome<info>735 B.C. corresponds to 1 A.U.C., or "ab urbe condita," which is Latin for "from the founding of the city." Romulus initiated a 304-day calendar of 10 months.
#e <t>calendar<d>700<n>January and February added<c>Rome<info>King Numa, Romulus' successor, adds Januaris and Februaris to the calendar, bringing it to 355 days. (Months had 29 or 30 days each, to correspond to the length of a lunar month.)
// Julian calendar
#e <t>calendar<d>46 May(2)<n>Julian reform<c>Rome<info>Julius Caesar orders a reform of the calendar, based on a proposal by the Alexandrian astronomer Sosigenes. He institutes a 365.25-day year, with a leap year every four years.
#e <t>calendar<d>46 Jan<e>46 Dec<n>"Year of Confusion"<c>Rome<info>46 B.C. was 445 days long. The new year was moved to January. (March had traditionally been the first month.) The traditional solstice had been March 25, so two months were added in between November and December to return it to its proper date.
#e <t>calendar<d>44<e>8<n>Leap years every three years<c>Rome<info>The Roman college of pontiffs strayed from Julius Caesar's decree, and began putting a leap year every three years instead of every four.
#e <t>calendar<d>8<e>A.D. 8<n>No leap years<c>Rome<info>Three leap years were skipped in order to correct the Julian calendar.
#e <t>coin<d>8<n>"August"<c>Rome<info>The Roman senate renames the eighth month, Sextilius, to August, in honour of Caesar Augustus. (Sextilius had been the sixth month before the new year was moved to January in 46 B.C.) They added a day to August to give it 31 like July, which honours Julius Caesar. The extra day was taken from February.
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#e <t>calendar<d>321<n>Romans adopt 7-day week<c>Rome<info>Constantine adopts the 7-day week for the Roman world, with Sunday as the worship day. Previously, the Romans had used an 8-day cycle to govern market days.
#e <t>calendar<d>531<n>A.D. dating system<au>Exiguus<info>Dionysius Exiguus introduces the "anno domini" (A.D.) dating system in a letter to bishop Petronius. Previously, the "anno Diocletiani," counting from the reign of emperor Diocletian, was commonly used. Dionysius wrote that he "preferred to count and denote the years from the incarnation of our Lord, in order to make the foundation of our hope better known and the cause of the redemption of man more conspicuous." Dionysius calculated that Christ had been born 531 years before, but how he arrived at this figure is unknown. It is generally accepted now that Christ was born between 6 and 4 B.C., according to this system.
// Gregorian calendar
#e <t>decree<n>Papal bull concerning calendar reform<c>Vatican<d>1582 Feb 24<info>This decree mandated the Gregorian calendar reform later that year.
#e <t>calendar<n>Gregorian calendar reform<c>Vatican<d>1582 Oct 15<info>October 15, 1582, was the first date of the Gregorian calendar. The preceeding day was October 4 in Julian calendar.
#e <t>calendar<d>2012 Dec 23<n>end of Mayan long-count calendar<c>Central America<info>The "great cycle" of Maya consists of 13 baktuns of 144,000 days each. The cycle began in about 3114 B.C.
