What the Julian Calendar Is

The calendar the Orthodox Church inherited is a Roman civil instrument, decreed by Julius Caesar and effective from 1 January 45 BC, with a year of exactly 365.25 days. This file sets out what it is, how the Church came to use it, what Pope Gregory XIII changed in 1582, and how the Orthodox East answered — including an honest account of a document that old-calendar polemic has leaned on far too heavily.

Tradition: Pan-Orthodox

Caesar’s Reform

The pre-Julian Roman calendar was a lunisolar mess, kept in rough alignment with the seasons by intercalations that the pontiffs inserted or withheld, sometimes for political reasons. By the middle of the first century BC it had fallen months out of step.

Julius Caesar, advised by the Alexandrian astronomer Sosigenes, replaced it with a purely solar scheme: a year of 365 days with an additional day every fourth year, giving a mean year of exactly 365.25 days. To bring the calendar back into line with the seasons, the year we call 46 BC was extended to 445 days — the annus confusionis, the “year of confusion” — and the reformed calendar took effect on 1 January 45 BC.

A note on dating, since the two figures both appear in this repository and elsewhere and can look like a contradiction: the reform was decreed in 46 BC and took effect in 45 BC. Both statements are correct and they describe different moments (see Orthodoxy: The Church Calendar, which gives 46 BC, and Orthodoxy: Calendar and Typikon in ROCOR, which gives 45 BC).

The intercalary day was inserted by doubling the sixth day before the Kalends of March — bis sextum kalendas Martias — from which English still has “bissextile” for a leap year. The pontiffs at first misapplied the four-year rule, counting inclusively and intercalating every three years; Augustus corrected the error by suspending intercalation for some years, and the calendar ran correctly from about AD 8 (Bickerman, Chronology of the Ancient World, 2nd ed., London: Thames and Hudson, 1980, pp. 47–51).

How the Church Came to Use It

The Church did not choose the Julian calendar. She was born inside it.

Every public act in the Roman Empire was dated by it, and the Church’s own acts were dated as everyone else’s were. There is no conciliar decision adopting it, no canon prescribing it, and no father arguing for it — because there was nothing to argue about (see Nicaea and the Independence of the Christian Reckoning). Its ecclesiastical use is a matter of continuous practice, not of legislation, and that is a distinction the rest of this collection will hold to.

Two Byzantine conventions grew up on top of it and are still visible in Orthodox usage:

The Indiction, a fifteen-year fiscal cycle beginning on 1 September, which became the start of the ecclesiastical year (see The Fixed and the Movable Year).
The era of Creation (Anno Mundi), which placed the creation of the world at 5508 BC and was the standard Byzantine and, until 1700, Russian year-count. Old Russian service books and chronicles date by it, and the Paschal tables are computed within it (Kuzenkov, Khristianskie khronologicheskie sistemy, Moscow: Russkii izdatel’skii tsentr, 2014).

The Gregorian Reform of 1582

The Julian year is about eleven minutes too long, and by the sixteenth century the accumulated error was about ten days: the equinox, which the Paschal tables placed on 21 March, was occurring around 11 March. The problem had been recognized for centuries — Bede noticed the discrepancy, and Roger Bacon and Nicholas of Cusa proposed corrections — but nothing was done until the Council of Trent authorized a reform and Pope Gregory XIII promulgated it.

The bull Inter gravissimas, dated 24 February 1582, did two things:

A one-time correction. Ten days were deleted: Thursday 4 October 1582 was followed by Friday 15 October 1582. Note that the weekday sequence was unbroken — a fact with more significance than it looks (see The Daily and Weekly Cycles).
A change to the leap rule. Century years would no longer be leap years unless divisible by 400. This gives a mean year of 365.2425 days, close enough to the tropical year to hold the equinox nearly still for millennia.

The Gregorian Paschalion followed the same three-clause Nicene rule but with corrected lunar tables (see How Pascha Is Reckoned).

Civil adoption was slow and followed confessional lines: the Catholic states in 1582–1584, the Protestant states over the following century and a half, Great Britain and its colonies in 1752, Russia in February 1918 (1 February became 14 February), and Greece in 1923. The distinction between the civil adoption of the Gregorian calendar and the ecclesiastical adoption of the Revised Julian is important and frequently blurred: Russia’s civil calendar has been Gregorian since 1918 while the Russian Church’s liturgical calendar has never ceased to be Julian.

The Orthodox Response, 1583–1593

Gregory XIII sent the reform to the East and pressed for its acceptance. The Ecumenical Patriarchate refused, and did so more than once. Three synods under Patriarch Jeremias II — in 1583, 1587, and 1593 — rejected the Gregorian calendar. The 1593 synod at Constantinople, whose acts survive and which is best known for confirming the establishment of the Patriarchate of Moscow, is the most securely documented of the three.

The reasons given were of two kinds, and they are worth reporting accurately because they are not what later polemic assumes:

Ecclesiological. The reform came as a unilateral act of the Roman pontiff, addressed to churches not in communion with him, in a period of active Latin proselytism in the East. Refusing it was of a piece with refusing the claims that accompanied it.
Paschal. The Gregorian Easter can fall before or together with the Jewish Passover, which the received Eastern discipline — in the form it had taken by the twelfth century, the “Zonaras proviso” — regarded as forbidden. This is a real concern of the sixteenth-century documents, and it is also, as How Pascha Is Reckoned explains, a discipline of later formulation rather than a Nicene rule.

What the synods did not do was define the Julian calendar as an article of faith. They rejected a specific reform, promulgated by a specific authority, for stated reasons.

The “Sigillion of 1583”

A text called the Sigillion of 1583 circulates widely in old-calendar literature. It purports to be a synodal act of Jeremias II with Sylvester of Alexandria and Sophronios of Jerusalem, and it carries eight sweeping anathemas — against the Filioque, azymes, purgatory, papal claims, and the calendar together — condemning anyone who follows “the calendar innovation of the Latins.”

Its authenticity is contested, and this library will not build on it.

[Disputed: one line of assessment holds the Sigillion to be a nineteenth-century composition, produced by the monk Iakovos of New Skete on Mount Athos in 1858 and back-dated (“Sigillion of 1583,” OrthodoxWiki, used as a locator per METHODOLOGY §2.3, citing the study “The ‘Sigillion’ of 1583 Against ‘the Calendar Innovation of the Latins’: Myth or Reality?”, Center for Traditionalist Orthodox Studies, imoph.org). A second line holds that the transmitted text is a compilation and synthesis of genuine documents and declarations of the period 1583–1616 rather than an invention, and that the underlying synodal condemnations of the Gregorian reform are historical whatever the status of this particular redaction (same study; and cf. “The Sigillion of the Council in Constantinople in 1583,” orthodox.net, which reproduces the text). What is not in dispute is that synods of 1583, 1587, and 1593 under Jeremias II rejected the Gregorian calendar.]

The distinction to hold is between the fact of the sixteenth-century refusal, which is well attested and which this collection relies on, and the anathemas of the circulated text, which are not securely attested and which this collection does not use. An argument for the old calendar that rests on the Sigillion’s anathemas is resting on a document that may not exist, and it invites a rebuttal that the underlying position does not deserve.