Pragjyotisas had an ethnological significance. They were a people of non-Aryan extraction. And the epics definitely describe the country of Pragyotisas as an Asura or Danava kingdom ruled over by the demons, Naraka and Muru, with whom the leaders of Aryanism were in frequent conflict. The Pauranic description of Naraka, the Asura leader, attributes to him immense power and a strength that baffled and perplexed even Indra. The environs of his capital city called Pragjyotisapura were defended by nooses constructed by the demon Muru. The Aryan leader, Krisna, is described as having got the better of the fight with the demons, which may be interpreted as one of the exploits in the history of the spread of Aryan influence in the east.
The Mahabharata in other places refers to Pragjyotisa as a Mleccha kingdom ruled over by a king named Bhagadatta who is always spoken of in respectful and even eulogistic terms. Bhagadatta is styled as Yavana, probably denoting that he did not belong to the Aryan fold. The Udyoga Parva has described him as the son of Naraka, the Pragjyotisa king, and as an ally of Duryodhana. Among his retinues Bhagadatta counted the Chinas. The Mahabharata has mentioned him as a king of boundless might ruling over Muru and Naraka.
According to the Mahabharata, Pragjyotisa was situated in the northern region of India but the Markandeya Purana places it in the eastern region, together with the Brahmottaras Pravijayas (perhaps Pravrseyas), Bhargavas, Madras, Videhas, Tamraliptakas, Mallas and Magadhas; or together with the Chandresvaras, Khasas and Magadhas. The mountainous regions called Antargiri, Vahirgiri, and Upagiri in the Mahabharata appear to comprise the lower slopes of the Himalayas and the Nepalese Terai; and it is not unlikely that the Pragjyotisas lived there contiguously. According to the Abhidhdnacintdmani, Pragjyotisa was the same as Kamarupa, though in the Raghuvamsa the Pragjyotisas and Kamarupas are described as two different people. Generally it can be said that the two countries came in later times to be regarded as one and the same. In the Kalika Purana, for example, the capital of Kamarupa is called Pragjyotisapura, which has been identified with Kamakhya or Guwahati. The Raghuvamsa seems to locate Pragjyotisa beyond the Brahmaputra River. For practical purposes, Pragjyotisa may, therefore, be identified with the whole of Assam proper, along with Northern Bengal as far as Rungpur and Cooch Behar, but the Ramayana has ascribed the foundation of the kingdom to Amurtarajas, one of the four great sons of King Kusa a significant Aryan name.
According to the Brahma Purana and the Ramayana, there seems to have been another Pragjyotisapura on the river Vetravati or Betwa. The later kings of Kamarupa, who claimed to have been descended from the line of Narakasura and Bhagadatta, figured prominently in Indian history.
History has recorded King Pralamba of Kamarupa as the ruler of Pragjyotisa. His grandson Vanamala claims to belong to the line (anvaya) of the lords of Pragjyotisa, and so also does Balavarman, another king of the same dynasty. During the earlier half of the eleventh century A.D., the capital city of Pragjyotisa seems to have attained great eminence under the kingship of Ratnapala.