History of Gujarat
The historians believe that this port might have named as Nagna or Nagnes due to the river Nagmati. Because Nag Jethva, the Jethva ruler, was not such a dominant gallant personality, from whose name the port could be named. The Nagnes port, Nageshwar Temple and the Nagmati River seem to have some co-relation. The Bhujang snake and Bhoriyoji’s famous love story also appears well consistent. In Nageshwar, the artistic memorial stone of Nag Devta is still there near the shrine of Mani Nagnath justifying the fact.

Foundation of Navanagar : Jurisdiction of Jam Rawal’s state kept on expanding as he kept on winning more and more regions. Jam Rawal earlier established the capital at Bed and then he shifted the capital to Khambhaliya. As the capital was far away from the Jodiya, Amran and Kalavad regions and as it was difficult to rule, Jam Rawal required establishing a new capital which should be in the middle of the region. So, Jamnagar, as the capital of the Navanagar state, was established on the banks of the river Nagmati and Rangmati on Wednesday, Shravan Sud Aatham, in Vikram Samvat - 1596.

A Volume namely Yaduvansh Prakash refers the establishment of Navanagar on Wednesday, Shravan Sud Satam in Vikram Samvat - 1596. Two or three pillars were planted at the time foundation of the capital. It is believed that of these, two pillars near Darbargadh and the third was planted near Mandvi Tower at present. One of the pillars exists in the Dilavar Cycle Store situated on the Rajendra road and the other one is believed to be in the house of Shri P. H. Sheth near Ram Hotel near the entrance of Darbargadh. The third pillar is presently not seen anywhere.

It is possible that in the initial period of the foundation might have been based upon this third pillar and the construction of the buildings might have been gradually made in the surroundings, extending up to the Mandvi Tower from Darbargadh, the Manek Stamph type pillar might have been planted at the time of laying the foundation. Shri Bhagvanlal Sampatlal, a historical author of Saurashtra, himself wrote in 1861 that Jam established Navanagar town in the month of Shravan at the place of Nagni. Though Jam named his capital as Navanagar, but the people called this city as Nagni only for a long time. Even today, the money changers and traders know this city as Nagni only.