The history of Orissa is over 3500 years old and has been mostly different from that of the rest of northers India.
In ancient times, it was known as Kalinga and was inhabited by a few large and prosperous tribes. As a major sea-faring nation, Kalinga had regular contacts with South and South East Asia. Merchants from Kalinga used to trade spices and other local products with other countries.
The Nanda Dynasty ruled over Kalinga from around 362 BC. Though Kalinga lost its independence, the Nanda rule brought prosperity to Kalinga through numerous developmental activities by the Nanda king.
In 261 BC, the Mayuran Emperor Ashoka invaded Kalinga. A fierce battle was raged at the banks of river Daya (now near to Bhubaneswar) which dragged over many days. The people of Kalinga resisted fearlessly, till their last resources were exhausted. There were a large number of soldiers slaughtered, from both armies, and the waters of river Daya was tinged red with the blood of the dead. At the end Ashoka won the war, but when he saw the devastation he had caused, it had a great impact on him. It led to the transformation of Ashoka, who was previously known as Chandashoka (the Cruel Ashoka), to be a kind and benevolent king known as Dharmashoka (the Pious Ashoka). He left the path of voilence and ensured good governance and ensured development in his empire.
That is what is depicted in the wall painting above which shows the armies fighting with the red tinged Daya river in the background and later Ashoka leaving the path of violence and embracing Buddhism by surrendering his sword to the Buddhist monks.
There's lot more on the history of Orissa. You can start from this Wikipedia article.
Back to the list of wall paintings in Bhubaneswar.