Long ago there was an 'asura' named 'Mahishaasura' who armed with the power of the boon Lord Brahma gave him created havoc on earth and in 'Swargam'(paradise). When the Gods approached Lord Brahma to save them from his tyranny he admitted that since it was his boon that gave him the power he could not do anything against it and suggested they plead Lord Vishnu. When Lord Vishnu heard their pleas he knew he alone could not destroy the demon so Brahma Vishnu and Maheswara(Shiva) combined their power and from their eyes a brilliant light emitted and converged at the ashram of rishi 'kaatyana'. From the brilliant light emerged 'Katyaayani' . The Mother proclaimed that she is the power who has created the universe and it is her energy that recides in Brahma, Vishnu and Maheswara. Then she rode on her lion and fought against Mahishasura. They fought for nine days and nine night before she slew the demon. Hence from 'padyami' to 'navami' the Navaratri is celebrated and during the tenth day The Durga Devi ia praised and puja is performed to conclude the celebrations.