Mercedonius (Latin for "Work Month"),[1][2][a] also known as Mercedinus,[3] Interkalaris[4] or Intercalaris (Latin: mensis intercalaris), was the intercalary month of the Roman calendar. The resulting leap year was either 377 or 378 days long. It theoretically occurred every two (or occasionally three) years, but was sometimes avoided or employed by the Roman pontiffs for political reasons regardless of the state of the solar year. Mercedonius was eliminated by Julius Caesar when he introduced the Julian calendar in 45 BC.
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