The proleptic Julian calendar is produced by extending the

Julian calendar The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts ...

backwards to dates preceding AD 8 when the quadrennial

leap year A leap year (also known as an intercalary year or bissextile year) is a calendar year that contains an additional day (or, in the case of a lunisolar calendar, a month) compared to a common year. The 366th day (or 13th month) is added to keep t ...

stabilized. The leap years that were actually observed between the implementation of the Julian calendar in 45 BC and AD 8 were erratic (see the

article for details). A calendar obtained by extension earlier in time than its invention or implementation is called the " proleptic" version of the calendar. Likewise, the

proleptic Gregorian calendar The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to the dates preceding its official introduction in 1582. In nations that adopted the Gregorian calendar after its official and first introduction, dates occ ...

is occasionally used to specify dates before the introduction of the

Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian cale ...

in 1582. Because the Julian calendar was used before that time, one must explicitly state that a given quoted date is based on the proleptic Gregorian calendar if that is the case. The Julian calendar itself was introduced by

Julius Caesar Gaius Julius Caesar (12 or 13 July 100 BC – 15 March 44 BC) was a Roman general and statesman. A member of the First Triumvirate, Caesar led the Roman armies in the Gallic Wars before defeating his political rival Pompey in Caesar's civil wa ...

, and as such is older than the introduction of the

Anno Domini The terms (AD) and before Christ (BC) are used when designating years in the Gregorian calendar, Gregorian and Julian calendar, Julian calendars. The term is Medieval Latin and means "in the year of the Lord" but is often presented using "o ...

era (or the "

Common Era Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar (and its predecessor, the Julian calendar), the world's most widely used calendar era. Common Era and Before the Common Era are alternatives to the ...

"), counting years since the

birth of Christ The Nativity or birth of Jesus Christ is found in the biblical gospels of Matthew and Luke. The two accounts agree that Jesus was born in Bethlehem, Palestine, in Roman-controlled Judea, that his mother, Mary, was engaged to a man named J ...

as calculated by Dionysus Exiguus in the 6th century, and widely used in medieval European annals since about the 8th century, notably by

Bede Bede (; ; 672/326 May 735), also known as Saint Bede, Bede of Jarrow, the Venerable Bede, and Bede the Venerable (), was an English monk, author and scholar. He was one of the most known writers during the Early Middle Ages, and his most f ...

. The proleptic Julian calendar uses Anno Domini throughout, including for dates of Late Antiquity when the Julian calendar was in use but Anno Domini was not, and for times predating the introduction of the Julian calendar. Years are given

cardinal number In mathematics, a cardinal number, or cardinal for short, is what is commonly called the number of elements of a set. In the case of a finite set, its cardinal number, or cardinality is therefore a natural number. For dealing with the cas ...

s, using

inclusive counting Counting is the process of determining the number of elements of a finite set of objects; that is, determining the size of a set. The traditional way of counting consists of continually increasing a (mental or spoken) counter by a unit for ever ...

(AD 1 is the first year of the Anno Domini era, immediately preceded by 1 BC, the first year preceding the Anno Domini era; there is no "zeroth" year). Thus, the year 1 BC of the proleptic Julian calendar is a leap year. This is to be distinguished from the

astronomical year numbering Astronomical year numbering is based on AD/ CE year numbering, but follows normal decimal integer numbering more strictly. Thus, it has a year 0; the years before that are designated with negative numbers and the years after that are designated ...

, introduced in 1740 by French astronomer

Jacques Cassini Jacques Cassini (18 February 1677 – 16 April 1756) was a French astronomer, son of the famous Italian astronomer Giovanni Domenico Cassini. He was known as Cassini II. Biography Cassini was born at the Paris Observatory. He was first admitted ...

, which considers each New Year an integer on a time axis, with

year 0 A year zero does not exist in the Anno Domini (AD) calendar year system commonly used to number years in the Gregorian calendar (nor in its predecessor, the Julian calendar); in this system, the year is followed directly by year (which is the ...

corresponding to 1 BC, and "year −1" corresponding to 2 BC, so that in this system, Julian leap years have a number divisible by four. The determination of leap years in the proleptic Julian calendar (in either numbering) is distinct from the question of which years were historically considered leap years during the

Roman era In modern historiography, ancient Rome is the Roman people, Roman civilisation from the founding of Rome, founding of the Italian city of Rome in the 8th century BC to the Fall of the Western Roman Empire, collapse of the Western Roman Em ...

, due to the leap year error: Between 45 BC and AD 8, the leap day was somewhat unsystematic. Thus there is no simple way to find an equivalent in the proleptic Julian calendar of a date quoted using either the Roman pre-Julian calendar or the Julian calendar before AD 8. The year 46 BC itself is a special case: because of the historical introduction of the Julian calendar in that year, it was allotted 445 days. Before then, the Roman Republican calendar used a system of intercalary months rather than leap days.

References

{{Calendars Julian calendar Specific calendars

See also

References