The Rath Yatra festival, popularly known as the procession of chariots, originated in the pilgrimage city of Jagannath Puri. Every year on Ashadh Sud Bij, the deities of Jagannath Mandir, namely Shri Krishna, Balaramji, and Subhadra Devi, are placed in a colorful chariot. Devotees lovingly pull the chariots in a procession through the streets. Hundreds of thousands of people gather to perform puja of the murtis by sprinkling rice and gulal powder.
The Rath Yatra festival is celebrated at BAPS Swaminarayan mandirs around the world. During this celebration, the small murti of Harikrishna Maharaj is seated in a chariot and is taken around the city or the mandir complex. Devotees pray to Bhagwan Swaminarayan asking Him to guide the chariots of their worldly lives across the ocean-like samsara.
Origins:
Several stories explain the origins of this festival:
Kansa, the maternal uncle of Shri Krishna, wanted to kill Shri Krishna and Balramji. Kansa invited Shri Krishna and Balramji to Mathura by sending Akrur to Gokul with a chariot. Shri Krishna and Balramji left the gopis in Gokul and climbed onto the chariot.
This day, commemorating their departure, is celebrated as Rath Yatra. – Shrimad Bhagavata Purana (10/39).
After Shri Krishna vanquished the evil Kansa, he gave darshan to devotees while sitting in a chariot with Balramji in Mathura.
When Shri Krishna was in Dwarka, on the west coast of Saurashtra, he took his sister, Subhadra, around the beautiful city in a chariot.
After Shri Krishna passed away, his bones floated to the shores of Jagannath Puri. Here, he gave darshan to the local king, Indradyumna, instructing him to collect the bones, put them behind a wooden murti, and build a mandir.