Athachamayam marks the beginning of the ten-day Onam festival in Kerala. It is an occasion to witness almost all the folk art forms of Kerala.

Conducted every year on the Atham asterism of the Malayalam month Chingam (Leo), the event held at the historical town of Thripunithura is a celebration of a legendary victory of the Raja (King) of Kochi. In olden days it was customary for the king to travel with his entire entourage to the Thripunithura fort. This was also the occasion for his subjects to greet the king and see him at close quarters. The procession, now without the king, still retains its majestic charm, and is conducted in a spectacular manner.

Caparisoned elephants, varieties of folk art forms, floats, musical ensembles etc form part of the procession.

Onam is the most popular festival of the Malayalees and can be traced to the primitive harvest festival and also to the myth regarding King Mahabali - the benevolent asura ruler who brought peace and prosperity to his country.