Mercedonius

Intercalary month of the Roman calendar

Mercedonius, also known as Mercedinus, Interkalaris or 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 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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