Sirmur was an independent kingdom in British India and presently situated in the area of Simaur district of Himachal Pradesh. It had an area of 1198 square miles. One of the popular theories says that during the late eleventh century, a destructive flood engulfed Sirmur town which might be the root cause of extinction of the royal family, priests, and nobles. The word ‘Sirmur’ is also spelled as Sirmor, Sirmaur, Sirmour, or Sirmoor. The state was also known as Nahan. The rulers of the Sirmur came from Rajut lineage. They used the title of ‘Raja’ and afterward ‘Maharaja’ which was given by the British. It lies between Balsan, Rajgarh and Jubbal in the North, Dehradun district in the East, Ambala district in the South West, and Patiala state and Keonthal state in the North-West.
Raja Karam Prakash founded the new state with a new capital and the state was named as Sirmur in 1616. The early history of Sirmur in not known. A legend says that its ancient capital was Sirmur whose king was Suraj Bansi or Solar race. According to one mythology, a woman was boasted by the king for her acrobatic talent. So, she was challenged by the king to cross and re-cross Giri River on a rope and in return she will be gifted half of his kingdom. The woman successfully crossed first lap. But when she was about to finish second lap, her rope was cut by the courtier in order to save the kingdom and she was drowned. Thereafter, the stream was flooded in which Sirmur, raja and his relatives swept away. They left the realm without any successor.
One of the other versions of legend says, Raja of Jaisalmer visited Haridwar and later he was invited by the minstrel of Sirmur to become its ruler. Later on, he came with the troops and controlled the sovereignty of the Sirmur under the title of Subhans Prakash. He founded Rajban town as a capital of the state in 1095. The eighth raja of same lineage conquered Ratesh region. His successors conquered Jubbal, Balsan, Kumharsain, Ghond, Kot, and Theog and extended their influence till Sutluj River.
In the history of Sirmur, capital of the state shuffled between Neri, Kot and Gargah in Ratesh Pargana. Later, Raja Budh Prakash sifted it to Kalsi.
However, Karm Prakash established Nahan as the modern capital in 1616. Mughal Emperor, Shah Jahan sought help from him for 2,000 horses to conquer Srinagar in Garhwal. Mandhata assisted Shah Jahan’s general Khalil Ullah in Gharwal invasion. His successor Sobhang Prakash received Kotah region as a reward for his service. His reign witnessed a great development of agricultural resources of the state and Kolagarh tract was also given to him by the Emperor. The next successor, Budh Prakash received Bairat and Kalsi forts from Raja of Srinagar which was originally of Sirmur.