An Intervening Adjustment That Errs Regarding The Timing of Christ's Birth

Taken from HERE

In the year 1278 AUC ( a b u rbe c ondita) * , meaning the number of years since the founding of Rome, Pope John I (Pope from 523 to 526 AD) commissioned Dionysius Exiguus ** , a monk and chronologist, to align the chronology of the date(s) of certain Christian holy days. Dionysius convinced Pope John I that the years of our calendar should start from the date of the birth of Jesus Christ. Dionysius determined (?) that Christ was born in the year 753 AUC. The Pope then decreed that the year 754 AUC was the year 1 Anno Domini (AD) and, it seems, he completely overlooked the fact that his innovation had Christ’s birth occurring after Herod’s death (4 BC) which is a contradiction of Matthew’s gospel . Dionysius also neglected to include a year zero "0" and his alignment started off the Christian era at year "1" (Even a child right out of the womb has to live for 12 months before he or she is considered a year old). Dionysius' error has never been corrected and 1 AD is actually "year zero" so everything in "BC" advances a year. This error has been incorporated into all of our astronomical and astrological software.
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The Christian era (AD), now used almost exclusively throughout the Western world for civil chronology, was first used in 525 AD by the Christian monk Dionysius Exiguus (c. 500-560 AD), who fixed the birth of Christ in the year of Rome 753. It is generally agreed that this date should have been fixed some years earlier. Dionysius's chronology was introduced into historical writings by Bede the Venerable in the 8th century.
© Copyright Simon & Schuster New Millennium Encyclopedia © 1998 Simon & Schuster, Inc.
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* In Roman chronology the era of the founding of the city (ab urbe condita, or AUC) dates from April 22, 753 BC, and the Julian era dates from the reform of the calendar by Julius Caesar in 45 BC., © Copyright Simon & Schuster New Millennium Encyclopedia © 1998 Simon & Schuster, Inc.
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** Dionysius Ex•ig•u•us \-eg-©zig-y¡-w¡s\. c.500–c.560. Scythian Christian monk and scholar. In Cyclus Paschalis (525) prepared for Pope St. John I, he introduced method of reckoning the Christian era (Dionysian period) which is still used, making the birth of Christ (incorrectly placed in year 753 of Rome) the starting point of modern chronology. © Copyright Simon & Schuster New Millennium Encyclopedia © 1998 Simon & Schuster, Inc.