Egyptian calendar, dating system established several thousand years before the common era
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[It] consisted of 365 days organized into 12 months of 30 days each [..] There was apparently no attempt to introduce a leap-year day to compensate for the slippage of one day every four years; as a result, the civil calendar slowly rotated through the seasons, making a complete cycle through the solar calendar after 1,460 years.
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The Egyptian civil calendar was altered by Julius Caesar about 46 BCE with the addition of a leap-year day occurring once every four years.