Tripurari Purnima is the full moon day in the Kartik month in a traditional Hindu calendar. Tripuri Purnima 2015 date is November 25. The popular belief is that to restore Dharma, Lord Shiva killed demon Tripurasura and destroyed the Tripuri or three cities built by him on the day. The day is also popularly known as Kartik Poornima.
Tripurari Purnima also marks the end of the month long Kartik Snan and vrat in
North India. The day also marks the end of the Kartik Brata in Orissa. The Tulvi Vivah rituals also end on the day.
Tripurari Purnima day is also observed as Dev Diwali in some regions. It is believed to be the Diwali of Devas as Lord Shiva liberated from the clutches of the oppressive rule of Demon Tripurasura.
Legend has it that a powerful demon named Tripuri or Tripurasura built three impregnable cities of gold, silver and iron with the blessing of Lord Shiva. The demon became so powerful and his inflated ego knew no bounds and started attacking and tormenting humans and demi gods (devas). Brahma and Vishnu failed to contain Tripurasura who was armed with several boons from Shiva.
Finally, the task of annihilating the demon fell on Lord Shiva and after three days of fight, Lord Shiva killed Tripurasura and destroyed the three cities – Tripuri. This great victory happened on the full moon day in Kartik month and therefore the day is celebrated as Tripuri Poornima.