The origins of the world famous Ratha Yatra of Lord Jagannath at Puri perhaps dates back to a time when Puri was called Danta Puri. The relic of Lord Buddha (a tooth) was worshipped by the Buddhists. There is a custom that the relics would be brought out every year in a chariot for all to see. Thus started the Ratha Yatra.
Earlier there was a river between the Jagannath Temple and the Gundicha Mandir. Therefore six chariots used to be built - three on each side of the river. Three boats used to carry the three images to the other side. The river was later filled up. Elephants were once an important part of the Ratha Yatra as the Kings of Puri (Gajapati Maharajas) were proud owners of magnificent elephants.
The Britishers were amazed at the huge crowds and the chariots being pulled within them seemingly out of control. They invented the term Juggernaut describing this phenomenon. They wrote that devotees used to commit suicide under the wheels of the chariots. But this was never true.
Earlier people used to travel by foot and Bullock carts from Bengal via the Jagannath Sadak. Remains of this road are still noticed today and my historian friend and classmate Anil Dhir has travelled, researched and written about this. Work is on to try and renovate this historical path. In Lord Chaitanyas time vaisnab devotees used to visit from Bengal during the Ratha Yatra and they still do.
It is believed that to witness the Lord on top of the Ratha delivers Moksha. Every year lakhs of devotees from all over the world gather to celebrate Ratha Yatra and express their whole hearted devotion to the Lord.