What does 312 mean in US Phone Area Codes?

312

Year 312 (CCCXII) was a leap year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Constantinus and Licinianus (or, less frequently, year 1065 Ab urbe condita). The denomination 312 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years. 312 (CCCXII) was a leap year starting on Tuesday of the Julian calendar, the 312th year of the Common Era (CE) and Anno Domini (AD) designations, the 312th year of the 1st millennium, the 12th year of the 4th century, and the 3rd year of the 310s decade. As of the start of 312, the Gregorian calendar was 1 day ahead of the Julian calendar, which was the dominant calendar of the time.

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