Shieldmeet

When the Netheril people lived on Toril they had leap years. On Dierde there are no leap years, but the tradition still survived. It is Celebrated on the last day of Firemonth .
  Traditionally the day was used for fairs, bazaars, musical and theatrical performances, and tournaments of skill and magical ability. Nobles usually held court to hear the petitions of their people and to make or renew trade pacts, alliances, and agreements.
  Shieldmeet was known as Cinnaelos'Cor (also seen as Cinnaeloscor), "the Day of Corellon's Peace" in elvish and marked the end of an aeloulaev and the beginning of a new one in the elven Aryselmalyn calendar.
  To carry on the tradition, it occurs every four years. it was not celebrated for some time, but since the year 0 it was reestablished and so it is celebrated every fourth year afterward.