LYCOS RETRIEVER 
Julian Calendar: Leap Years
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With the introduction of the Julian calendar a period of almost complete disorder in the Roman calendar came to an end. Until then, the beginning of the month was announced at the first visibility of the moon's crescent after new moon, though the year was reckoned depending on the sun. The lengths of the years in a four year cycle of this lunisolar calendar were 355, 377, 355, and 378days, which was almost four days longer than the true length of four years. Soon the calendar derailed because of leap years introduced to keep it aligned with the sun. In 47BCE, the calendar was in error by about three months.
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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,"[14] a total that could only have been counted with the aid of the uniform Julian calendar.
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When it comes to determining if a year is a leap year, since AD8 the Julian calendar has always had 48 months between two leap days. So, in a country using a year starting on 1March, 1439 would have been a leap year, because their February1439 would correspond to February1440 in the January-based reckoning.
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Although the new calendar was much simpler than the pre-Julian calendar, the pontifices apparently misunderstood the algorithm for leap years. They added a leap day every three years, instead of every four years. According to Macrobius, the error was the result of counting inclusively, so that the four year cycle was considered as including both the first and fourth years. This resulted in too many leap days. Augustus remedied this discrepancy after 36 years by restoring the correct frequency. He ... skipped several leap days in order to realign the year.
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[T]he 4-year rule was not followed in the first years after the introduction of the Julian calendar in 45BC. Due to a counting error, every 3rd year was a leap year in the first years of this calendar's existence. The leap years were:
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Leap Years