Athachamayam is a grand cultural fiesta marking the beginning of the ten-day Onam Festival in Kerala. Celebrated annually on the Atham asterism of the Malayalam month of Chingam (August/September), the event takes place in Thripunithura, near Kochi, in Ernakulam district. This legendary ceremony commemorates the victory of the Raja (King) of Kochi, showcasing almost all the folk art forms of Kerala.

The celebration is highlighted by a magnificent procession representing the King and his entourage. The parade includes caparisoned elephants, vibrant floats, musical ensembles, and a variety of folk art forms, creating a colorful and lively atmosphere. The Athachamayam parade held in Thripunithura has a rich historical significance, as it was once the headquarters of the Maharajas of the Cochin state. Before independence, the Maharaja of Cochin would visit his subjects with his entourage, making the event a symbol of the royal legacy.

In 1949, the event was temporarily halted due to the merging of the Travancore-Cochin kingdoms to form the Thiru-Kochi state. However, it resumed in 1961 when Onam became a mass festival in Kerala. Today, the procession starts from Attam Nagar, near the high school ground, and concludes there.

The royal Athachamayam is preceded by a three-day ritual. The royal town crier arrives in the village on an elephant, beats the drum to attract the villagers' attention, and announces the start of the rituals. Symbolizing religious harmony, the Kakkattu temple priest, Nettur Thangal, and the priest of Karingachira visit the king on the day of the parade. The king, adorned in vibrant jewels known as ‘veeralipattu’ and wearing a golden crown, enters the palanquin to begin the parade. After the procession, a lavish sadya (feast) is held, followed by an awards ceremony to recognize outstanding locals.

Folk stories add to the charm of Athachamayam. One such tale relates to the Thrikkakkara Vamana Moorthi Temple, where the festival was initially conducted through the combined efforts of 56 kings, with the Athachamayam procession led by the Maharaja of Cochin and the Samoothiris. Another folklore recounts the remembrance of a revolt when the Maharaja of Cochin tried to capture the land of Vanneri from the Samoothiris. Historical accounts also claim that the parade commemorates the King's victory in the Battle of Kochi.

Athachamayam evokes memories of bygone eras and stands as a symbol of religious unity, drawing people from all walks of life to celebrate the rich cultural heritage of Kerala.