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A.U.C. is an abbreviation for ab urbe condita, “from the founding of the city” of Rome. The year 1 A.U.C. is the same as the year 753 B.C., The year 1 B.C. is the same as the year 753 A.U.C., and the year 1 A.D. is the same as the year 754 A.U.C.. Unfortunately, a year divisible by 4 in the Roman calendar is not divisible by 4 in the Christian calendar. As an example, the year 4 A.D. is divisible by 4. The equivalent year by the Roman calendar is 757 A.U.C., which is not divisible by 4. This is very inconvenient when figuring leap years.