Onam has been a part of Malayalee culture for centuries. The earliest record of the festival that has been found belongs to the reign of Kulasekhara Perumals around i.e. around 800 AD. However, there are great possibilities that the festival was celebrated before this period also. Any ways, due to lack of physical evidences, it has been assumed that the festival started somewhere around 800 A.D. as the harvest festival of the state. However, there are so many legends and stories attached with the day that it seems that the festival has been a part of the region ever since its origin.
Onam Celebrations has two most important significances in context of the Malayalee culture. First of all, it is celebrated as the harvest festival of the state. It reminds one of the golden age of prosperity when the entire month of Chingam (the month of Malayalee calendar that corresponds to the August- September time of Gregorian calendar) was celebrated as the Onam month. It was the time when the farms of the state produced excess of food grains and brought prosperity and riches to the state. Arriving after the rain-drenched month of Karkidakam (July-August), Chingam was welcomed with much enthusiasm by the people of Kerala.
The second and the most popularly quoted legend with the festival is related to the demon king, Mahabali. It is said that Mahabali was a generous and kind hearted king of Kerala. He was powered by a boon granted to him by Lord Brahma, he was invincible and thus gradually won over the entire earth. Soon after he won the earth, he also won the territory of heaven and became its king. He gradually rose up to become the undisputed ruler of all the three worlds. It was the time he inflicted violence upon the gods. Lord Vishnu then decided to overthrow Bali from his powers. He went to Bali in the form of a Brahman as he knew that the king rejoiced in doing good deeds and giving alms to the poor. He asked for three feet of land from the Demon king to which the king readily agreed.
Gradually, he Brahaman increased in size. In one step, he measured the entire earth and in the other he covered the entire heaven, he then asked Bali that where should he put the third step. Bali, a man of his words, then laid down his head and asked Brahman to step his foot on his head. Vishnu disguised in the form of Brahman, thus appeared in front of Bali and offered him the Kingdom of the nether world. However as Bali was very much in love with the people of his kingdom at earth, he asked Vishnu to give him a boon so that he can visit the earth once a year to which Vishu readily agreed. Bali, since then is believed to come to earth in the month of ‘chingam’ according to the Malayalee calendar and the entire festival is celebrated to welcome their dear king Mahabali to earth.