The origin of our everyday calendar reaches back to the time when Roman military expansion spearheaded by Pompey first encircled the Mediterranean. Julius Caesar, in his turn, defeated Pompey. After the downfall of Pompey new storehouses of astronomical knowledge were opened to Caesar, who emerged as the first imperial ruler over the entire Roman world. Caesar eagerly applied this newfound knowledge to the failing Roman old-style calendar, and produced for the first time in the Roman world a stable and accurate timekeeping system to meet the needs of a growing empire.[1,2]
The Roman old-style calendar harkened back to the very foundation of Rome in the days of the famous twin brothers, Romulus and Remus, who were said to have been suckled by a wolf under the shelter of the sacred fig tree on Palentine hill. This primal calendar consisted of ten lunar months with seven months of thirty-one days and three months of twenty-nine days. The year lasted 304 days so that there were an exact number of eight-day weeks in the year. This was done due to Roman regard for the number eight. The apparent purpose of having thirty-one days instead of a more sensible thirty days was to have a distinct day for the "ides" or middle of the month. The year began with the sighting of the first crescent moon after the spring equinox. After awhile, the official opening of the year was moved forward, and the months of January and February were added to the calendar. Since the total number of days in a twelve-month lunar calendar (354 days) are a little more than eleven days short of a solar year, an intercalary month, known as Mercedinus, of either twenty-two or twenty-three days was added once every two years. In this way, the Feast of Terminalia had been celebrated as the last day of the year.
The high priest, or Pontifex Maximus, was charged with regulating the calendar. This entailed inserting the intercalary month when necessary and watching for the crescent new moon. When the crescent moon first appeared the high priest would proclaim the beginning of the month. The Latin word for "proclaim" is "calare" so the first day of the month came to be known as the "calends".
Another key day, called the "nones" (ninth), broke up the interval between the calends and the ides. Tracking time, day after day, during the course of the month was accomplished by counting down towards the next important day. Thus, if one started counting on, say, "the third day before the ides of March", the next day would be "the eve (or the second day) before the ides of March", which in turn would be followed by the "ides of March".
On the whole, regulating the old Roman calendar proved to be quite disorderly. Serious lapses occurred during the period of civil disorder during the last days of the Roman Republic. Consequently, when Julius Caesar emerged victorious over the republican forces, Caesar exercised his duty as Pontifex Maximus and enlisted the help of Sosigenes, a Greek astronomer living in Alexandria, to restructure the Roman calendar. Sosigenes recommended a calendar of 365 days similar to the Egyptian calendar, but with the addition of an intercalary day being added to the calendar every fourth year. This modification to the Egyptian year revived a similar scheme, known as the Decree of Canopus (238 BCE), which had been issued at the time of Ptolemy III, who reigned over Egypt some two hundred years before the time of Sosigenes. The fourth year, or leap year, in the new Roman calendar would contain twelve months with an extra intercalary day added in the month of February. In a common or hollow year of 365 days, the month of February was assigned its normal allotment.
The last year (46 BCE) of the traditional Roman calendar was extended by necessity to a length of 445 days. Twenty-three days were added to February in the customary style and another sixty-seven days were inserted between November and December. This year that bridged the commencement of Caesar�s reign with the preceding years of calendrical confusion became known as the "Last Year of Confusion" or more simply as the �Year of Confusion�. The calends of January, the first day into the new calendar, started off on a day the evening of which saw the occurrence of a new moon. The first year was counted as a leap year so February received its full count with the extra day for the month being added immediately after the Feast of Terminalia, that is February twenty-third. The months of March, April, May, June, Quintilis, Sextilis, September, October, November, and December followed in their normal succession.
Some of the leading senators of the day, already unhappy with the Caesar's dictatorial rise to power, schemed to assassinate Caesar. The Julian calendar, which parted from well-established Roman tradition and fashioned after the Egyptian manner, created one more irritation. Assassination plots circulated among the senators. A short time into the second year of the calendar (44 BCE), within the latter part of February, Caesar received a forewarning from a prominent astrologer that his life would be in danger during the approaching month.
Caesar appeared to be relatively unconcerned about the warning. On the last day of this ominous period coinciding with the ides of March, he entered the Forum for the last time. Several of the Senators attacked him with daggers. Everyone fled the scene when the atrocity was finished. Caesar's body, abandoned by both his friends and enemies, rested on the floor with a count of twenty-three bleeding stab wounds. The tally left a cutting reminder on the dead body of the Pontifex Maximus - an intercalary count of twenty-three days had regulated the traditional Roman calendar.
The reading of Caesar's will declared his young nephew of nearly nineteen years of age, Octavian (who later adopted the name "Augustus"), as heir to the imperial legacy. Battles ensued to determine the future course of Roman affairs. The republican conspirators were defeated so that the Julian calendar survived, and the month of Quintilis was renamed Julius (July). In the interim shortly after Caesar's death, an auspicious comet appeared during the Olympic Games. A comet was usually interpreted as a disastrous sign of ill boding, but Octavian capitalized on Julius Caesar's enduring popularity among the soldiers, and acknowledged the comet as a special sign showing the acceptance of Caesar's rising soul into heaven.
This Silver denarius issued (19-18 BCE) by Augustus Caesar shows the 44 BCE comet of "Divine Julius," which was propagandized as a good portent. Illustration furnished by Michael R. Molnar as shown in his book, "The Star of Bethlehem, The Legacy of the Magi."
According to the Roman historian Suetonius, Octavian, while still shy of his twentieth birthday, convinced himself about the wisdom that emanated from the stars. Suetonius describes an event that occurred a very short time before Caesar's death, when Octavian and his long-term supporter Agrippa consulted an astronomer named Theogenes. "Agrippa was the first to try his fortune, and when a great and almost incredible career was predicted for him, Augustus (Octavian) persisted in concealing the time of his birth and in refusing to disclose it, through diffidence and fear that he might be found to be less eminent. When at last he gave it unwillingly and unhesitatingly, and only after many urgent requests, Theogenes sprang up and threw himself at his feet." Theogenes did not leave any details as to just what had prompted his reaction, but the fact that Jupiter, the master of sea and sky, was positioned under Praesepe, the manger in Heaven, and located in opposition to the moon, while Mars, the patron of Rome, was in the middle of an encirclement of the planet Saturn, the patron of Palestine, could only contribute to his sense of awe. From that moment, Augustus overcame his reluctance to divulge the time of his birth, and appears anxious to pursue his destiny as manifest by the stars. Sometime later, when Augustus had already reached the zenith of his power, he made his horoscope public and issued a silver coin stamped with the sign of the constellation Capricorn, under which [the moon stood when] he was born.
This silver cistophorus (27-26 BCE) shows Augustus's sign, Capricorn, holding a cornucopia signifying great bounty bestowed upon Augustus by his horoscope. Illustration furnished by Michael R. Molnar as shown in his book, "The Star of Bethlehem, The Legacy of the Magi."
After the defeat of the republican conspirators, a new and effective ruling regime was formed consisting of the Triumvirate: Octavian, Mark Antony, and Lepidus. Lepidus received the title of Pontifex Maximus, and attempted to regulate the calendar. The fourth year into the Julian calendar saw an inadvertent second leap year. In a cyclical count of this kind the last year was commonly counted as being identical with the first year in the succeeding count. The first and fourth years were, therefore, enumerated as the same year. This cyclical method of reckoning leap years resulted in a leap year mistakenly being assigned once every three years instead of once every four years.
The unity among the members of the Triumvirate began to crack even as the calendar and the seasons slowly drifted apart. A power struggle ensued once again, and Octavian emerged victorious. Lepidus fell from power when an attempted takeover against Octavian failed. Lepidus managed to hold onto both his life and the office of Pontifex Maximus, but he languished in exile. Mark Antony did not fare as well. Antony lost his popularity among the Roman Legions as he entwined himself with Cleopatra and assimilated more and more of the foreign Egyptian culture. Mutual animosity was enflamed by both Antony and Octavian, bringing about a final confrontation. In the end, after the defeat of the forces led by Antony and Cleopatra in the naval battle off Actium, the unfortunate pair committed suicide. The date was recorded as occurring within the month of August, which belonged to the fifteenth year of the Julian calendar (31 BCE).
Members of the Senate reconciled themselves to Octavian's unchallenged position of power and awarded him the name of Augustus. The calendar, however, for more than another twenty years, remained under the auspices of Lepidus until the time of his death. At that time, some thirty-six full years after the Year of Confusion, twelve leap years had been counted instead of nine. Augustus promptly corrected the deviation. No leap days were added for the next twelve years. The month Sextilis was renamed Augustus to show its special significance as the eighth month in the new calendar year and to provide Augustus with the same honor already awarded to Julius Caesar. At about this same time, the Greek provinces of Asia Minor chose to honor Augustus by adopting a uniform solar calendar in place of their various lunar calendars, wherein they displayed their respect by starting the calendar year with the birth date of Augustus and named the first month of the year "Kairsarios".
The revised Julian calendar finally arighted itself on first day of March belonging to the 45th year of the Julian calendar (1 March 1 CE). The proper count for leap years had resumed once more after a forty-four-year hiatus. Augustus continued to rule up until the day of his death, which can be reported as the 19th day of August belonging to the 57th year of the Julian calendar or, alternately, the fourteenth year of the readjusted Julian calendar (19 August 14 CE). His extended reign was said to have lasted fifty-six years. His life span was nearly seventy-six full years. According to Cassius Dio, a Roman historian of the period, the duration of his life was "seventy-five years, ten months and twenty-six days," a total that could only have been counted with the aid of the uniform Julian calendar.
Even though Augustus seemed to have lived his entire life under the influence of a favorable star, he could not deter the hand of misfortune from stealing away his closest companion. Augustus grieved deeply when Agrippa, his lifelong friend who had early on introduced Augustus to the world of astrology, died as a comet hung over the Roman capital near the end of August (12 BCE). This comet appeared to effect Augustus very differently than the one, which appeared some thirty-three years earlier when he had exclaimed how a comet that shone shortly after the time Caesar�s death signified the rising of Caesar�s soul into heaven.
The Julian calendar managed to integrate itself as part of Roman culture during the reign of Augustus. Still, even with all the attention Augustus had directed towards the Julian calendar, the calendar retained a serious problem. The problem arises from the fact that the length of the Julian calendar year does not exactly match the length of the solar year. A solar calendar keeps time according to a tropical year, which is defined to be the time required by the sun to travel a complete circuit starting with the vernal equinox. The mean calendar year of 365 days and six hours is just short of a tropical year, so that the date for the equinoxes and the solstices fall three days earlier over a course of four centuries.
The effect of the sliding calendar drew a reaction after several centuries. Various clerics, who convened at Emperor Constantine's invitation at the Council of Nicea14 in the 325th year of the corrected Julian calendar acknowledged the shift in the calendar, but didn't understand the reason. They recognized that a problem existed, but corrected it by simply declaring March twenty-first as the actual day for the vernal equinox instead of the traditional March twenty-fifth.
 Plutarch, The Fall of the Roman Republic, Six Lives by Plutarch, translated by Rex Warner, Caesar, , pg 298, Penquin Classics
 Suetonius, The Twelve Caesars, Julius Caesar, translated by Robert Graves, ,
pg 27, Penquin Classics
 Pliny, Natural History 18, 57. 210f.
"... There were three main schools, the Chaldaean, the Egyptian, and the Greek; and to these a fourth was added in our country by Caesar during his dictatorship, who with the assistance of the learned astronomer Sosigenes (Sosigene perito scientiae eius adhibito) brought the separate years back into conformity with the course of the sun."
 Cassius Dio, History of Rome, XLII, 26.1-2
 Six Lives by Plutarch, [67c], pg 306
 Cassius Dio, History of Rome, XLV, 7.1
"... A certain star appeared in the north toward evening, which some called a comet, claiming it foretold the usual occurrences, while the majority, instead of believing this, ascribed it to Caesar, interpreting it to mean that he had become immortal and had been received into the number of the stars."
 The Twelve Caesars, Julius Caesar,  pg 48
 The Twelve Caesars, Augustus, [94l], pg 103
 Cassius Dio, History of Rome, XLII, 26.3
 Macrobius, Saturnalia I.14.13, translated by P. V. Davies,
"Caesar�s regulation of the civil year to accord with this revised measurement was proclaimed by edict, and the arrangement might have continued to stand had not the correction itself of the calendar led the priests to introduce a new error of their own; for they proceeded to insert an intercalary day, which represented the four quarter-days, at the beginning of each fourth year and before the beginning of the fifth. The error continued for thirty-six years, by which time twelve intercalary days had been inserted instead of the number actually due, namely nine. When this error was at length recognized, it, too, was corrected by an order of Augustus that twelve years should be allowed to pass without an intercalary day, since a sequence of twelve such years would account for those three years too many which, in the course of thirty-six years, had been introduced by the premature action of the priests. After that, one intercalary day, as ordered by Caesar, was to be inserted at the beginning of every fifth year, and the whole of this arrangement of the calendar was to be engraved on a bronze tablet, to ensure that it should always be observed."
 The Twelve Caesars, Augustus, , pg 67
 The Twelve Caesars, Julius Caesar,  pg 41
See also Macrobius, Saturnalia I.12.34,
"... although it [Quintilius] was then, clearly, no longer the fifth month but the seventh. Subsequently, however, in pursuance of a law proposed by Marcus (son of Marcus) Antonius as consul, the month was called July in honor of the dictator Julius Caesar, because he was born on the twelfth day of this month."
 See The Origins of the Liturgical Year, by Thomas J Talley pg 8, which in footnote 7 refers to Mateos, Le Typikon, Tome I, p. 55.
 Cassius Dio, The Roman History, Book 56.30
 Cassius Dio, The Roman History, Book 54.39
"Agrippa's death was felt not only as a private bereavement for his family: it was regarded as so much of a public loss to the whole Roman people that portents were noticed at that time in such numbers as normally occur when the greatest calamities threaten the state.
"... The star known as the comet hung for several days over the capital, and finally dissolved into flashes of light resembling torches. Many buildings in the city were burned down ..."
This comet has been identified as Halley's comet and was reportedly first sighted at about 25 August 12 BCE according to Hughes, "The Star of Bethlehem".
 In spite of the efforts put forward by the Nicean Council and Dionysius, the tabulated date for Easter continued to cause confusion until the time of the Gregorian calendar reform. Another correction occurred when 10 days were skipped, and the Julian date, 5 October 1582, was reassigned to 15 October 1582 on the Gregorian calendar. The seasons continue to stay properly aligned with the Gregorian calendar, because Pope Gregory XIII decreed that every century year, such as 1700, 1800, or 1900, not divisible by four would not be a leap year. As a result, spring now occurs regularly around March twenty-first. In England, in the year 1800, where the date for spring of March 25th had marked the beginning of the religious calendar year, the religious New Year�s date was then transferred to April 6th on the Gregorian calendar. As happenstance would have it, this date of April sixth (the fourteenth day of Artemisios) falls precisely nine months before January sixth and had already been designated as a critical quarter-tense day by the early Christians of Asia Minor.
What has become known as the Christian era was first initiated two hundred years after the Council of Nicea by a Roman abbot, Dionysius Exiguus, who worked out a cyclical table to determine the proper dates for Easter. The table marked off the calendar dates for the first Sunday, following the first full moon, following the vernal equinox, for a cycle of 532 years. Dionysius reckoned the cycle length as the product of nineteen, the number of years in a Metonic Cycle, times twenty-eight, the number of years in a dominical cycle. The completion of the first cycle as measured against the revised Julian calendar was only seven years removed from the time when Dionysius worked out his Easter table. Somehow, during his deliberations Dionysius was able to declare the first year in the Easter table, which coincided exactly with the first year of the revised Julian calendar, as the self same first year of the Christian era. The specific method with which this feat was achieved continues to puzzle Christian and historical scholars.