The Mahasivarathri is essentially a religious festival unlike the Onam and Thiruvathira. The word means `the great night of Siva. According to the Sivapurana, it falls on the Krishna Chathurdasi day which is on the fourteenth day during the warning of the moon in the month of Megha, though in some years it may occur in Phalguna also. In Kerala the month of Kumbham is noted for the Sivarathri festival which falls in February -March.

The festival is said to commemorate the day on which Siva protected the world from a total annihilation either by drinking the deadly Kaalakoodum poison which was held up in his neck, or by effecting a healthy compromise between Brahma, the Creator and Vishnu, the Protector.

The Mahasivarathri is considered a very important day for fast and Siva worship.

Though the observance of Sivarathri rites promises both material comfort in this world and bliss in the other, it is mainly observed for securing the latter, While some Hindus abstain from every kind of food for the whole day, others content themselves with one meal. People cluster round the Siva temple and after bath smear their bodies with holy ashes and keep on reciting the prayers to siva. Pooja to Siva is kept up all the night. Strict vigil is kept in the holy night. Early next morning people bath once more, worship Siva and return to there are Siva temples where Kavadiyattom is of great significance in the celebration of the Sivarathri festival.

There is no other place in Kerala where Sivarathiri is celebrated on such a grand scale as in Aluva. The celebration of Sivarathri in Aluva is as famous as the festivals like Ashtami at Vaikom, Pooram at Thrissur etc. The celebration of Sivarathri at the Siva temple at Aluva on the sand bank of River Periyar is attended with great eclat. Here the Lingom (idol) of Siva rises out of the sand on the bank of the river. The sand bank is extensive and the pilgrims running into several thousands congregate here. People belonging to all classes, castes and creeds assemble for this festival, some for worship, some for merchandise and some for sight-essing. There are rows of sheds built where merchants exhibit every kind of merchandise for sale. There are shows, dances etc. meant for keeping the pilgrims awake throughout the night. In addition to the observance of Sivarthri rites, most of the pilgrims offer Bali (sacrifice) to their ancestors in the morning succeeding the holy night.

In many respects the Sivarathri festival in Kerala can be considered a miniature Ardha Kumbha Mela held at Thriveni, the confluence of the holy rivers Ganga-Yamuna, and the invisible Saraswathi.