[8][9][5][10] Onam commemorates the return of the generous daitya king Mahabali after he was banished to the netherworld by Vamana (the fifth avatar of Hindu deity Vishnu).

The king Mahabali (himself a devotee of Vishnu) conducts ritual prayers, one of which is attended by Vamana, who requests only three feet (steps) of land to build a fire-altar.

[15][16] However, witnessing Mahabali's love for his subjects, Vamana grants the king's sole wish to visit his kingdom once every year.

[19] Literary and epigraphical evidence suggests that Onam has a long religious context and history in Kerala and neighbouring parts of South India:[19] चोकुयन्ते पृथुकततयश्चापतादिन्य उच्चैः सर्वानार्यःपतिभिरनिशम् लम्भयन्त्यर्थकामान्। बभ्रम्यन्ते सकलपुरुषैर्वल्लभाभ्यः प्रदातुम् चित्रम् वस्त्रम् श्रावणकुतुकम् वर्तते केरळेषु॥ Gangs of lads, playing their bows hoot loudly again and again; All women make their husbands provide wealth and pleasure; All men are wandering hither and thither to present beautiful garments to their women.

According to Hindu mythology, Mahabali was the great-great-grandson of a Brahmin sage named Kashyapa, the great-grandson of a demonic dictator, Hiranyakashipu, and the grandson of Vishnu devotee Prahlada.

This revisit marks the festival of Onam, as a reminder of the virtuous rule and his humility in keeping his promise before Vishnu.

The story is significant not because Mahabali's rule ended, but it emphasises the Hindu belief in cyclical nature of events, that no individual, no ruler and nothing lasts forever, except the virtues and self-understanding that overcomes all sorrow.

[31] An alternate tale behind Onam relates to Parashurama, an incarnation of Vishnu who is credited in Hinduism to have created the Western Ghats and Kerala.

[32] According to this legend, Vishnu observed the kings of the Kshatriya (warrior) waging constant war on one another and growing arrogant.

[32] Following the murder of his father Jamadagni, Parashurama swore vengeance against the king and the warrior class, slaying them as he travelled the world.

[32] Onam is a "popular major Hindu festival in Kerala", states Christine Frost, but one that is also celebrated by other communities with "much zest alongside Hindus".

[34] The festival is celebrated in BECs (Basic Ecclesial communities) in Trivandrum with local rituals, according to Latin Catholic Bishop[35] Selvister Ponnumuthan.

[36] These traditions, according to Selvister Ponnumuthan, start with the lighting of Nilavilakku, an arati that includes waving of flowers (pushparati) over the Bible, eating the Onam meal together with the Hindus as a form of "communion of brothers and sisters of different faiths".

[36] The significance of these practices are viewed by BECs in Trivandrum as a form of integration with Hindus, mutual respect and sharing a tradition.

The ten days are sequentially known as Atham, Chithira, Chodhi, Vishakam, Anizham, Thriketa, Moolam, Pooradam, Uthradam and Thiruvonam.

This Vishnu temple is considered as the focal centre of Onam and the abode of Mahabali, with the raising of the festival flag.

[47] Other days have a diverse range of celebrations and activities ranging from boat races, cultural programs, sports competitions, dance events, martial arts, floral Rangoli – pookkalam, prayers, shopping, donating time or food for charity to spending time with family over feasts.

[48] The Onam celebrations across the state starts off with a grand procession at Thrippunithura near Kochi called Atthachamayam, also referred to as Thripunithura Athachamayam.

The parade features decorated elephants marching, drum beats and other music, folk art forms, floats and colourfully dressed people with masks.

[49] In Kerala's history, the Kochi king used to head a grand military procession in full ceremonial robes from his palace to the Thrikkakara temple, meeting and greeting his people.

It is a work of religious art, typically the team initiative of girls and women, who accomplish it with a delicate touch and a personal artistic sense of tone and blending.

[56] Earthen mounds, which look somewhat like square pyramids, representing Mahabali and Vamana are placed in the dung-plastered courtyards in front of the house along with the Pookalam, and beautifully decorated with flowers.

[47] Traditional dance forms including Thiruvathira, Kummattikali, Pulikali, Thumbi Thullal, Onam Kali and others.

[citation needed] Kathakali dance is also commonly performed during this time, with dancers enacting characters from the various Ancient Indian legends.

[citation needed] At the Thrikkakara temple, every day of the festival showcases one or more of these activities including Kathakali, Thiruvathira, Chakyar Koothu, Ottam Thullal, Patakam, Onam songs, and percussion instrument shows.

The official Government celebrations start on this day with heavy illuminations in Thiruvananthapuram, Kochi and Kozhikode along with fireworks.

[citation needed] Most cities in Kerala, such as the political, commercial and cultural capitals, Thiruvananthapuram, Kochi and Thrissur, are lit up with lights and fabulous displays of fireworks.

[65] The feast is served on plantain leaves and consists of nine courses, but may include over two dozen dishes, including (but not limited to):[66] Chips (especially Banana chips), Sharkaraveratti (Fried pieces of banana coated with jaggery),[67][68] Pappadam, various vegetable and soups such as Injipuli (also called PuliInji), Thoran, Mezhukkupuratti, Kaalan, Olan, Avial, Sambhar, Dal served along with a small quantity of ghee, Erisheri, Molosyam, Rasam, Puliseri (also referred to as Velutha curry), Kichadi (not to be confused with Khichdi) and Pachadi (its sweet variant), Moru (buttermilk or curd mixed with water), Pickles both sweet and sour, and coconut chutney.

The feast ends with a series of dessert called Payasam (a sweet dish made of milk, sugar, jaggery, and other traditional Indian savouries) eaten either straight or mixed with ripe small plantain.

Young men and women, decked in their best, sing Onappaatt, or Onam songs, and rock one another on swings slung from high branches.