As per wish of Swargadeo Rudra Singha from his deathbed, he was succeeded by his eldest son Siba Singha. Siba Singha ascended the throne and assumed the Ahom name Sutanphaa. He gave up Rudra Singha's plan to organise a confederacy of the rajas of Hindustan and to invade Bengal, but obeyed his father's injunction to become a disciple of Krishnaram Bhattacharjya the Shakta priest from near Nabadwip in West Bengal. He gave the management of the Kamakhya Temple to Krishnaram, who came to be known as Parbatiya Gosain, as his residence was on top of the Nilachal hill. Siba Singha accepted him as the royal priest and made large number of land grants to temples and the Brahmin priests.
His long 30 years reign was peaceful, only in January 1717 there was an expedition against the Daflas of the northern hills, who had again taken to raiding the plains people. After they had been reduced to submission, an embankment was constructed along the foot of the hills inhabited by them as protection against future raids.
Bar Rajas
Siba Singha was a staunch Shakta and was greatly influenced by the Brahmin priests and astrologers. In 1722 he was so alarmed by their prediction that his rule would shortly come to end, that he not only made many and lavish presents to various temples and the Brahmins, in hope of conciliating the gods and averting the calamity, but also endeavoured to satisfy the alleged decree of fate by a subterfuge which greatly diminished his prestige in the eyes of his people. He declared his chief queen Phuleswari, who assumed the name Pramateswari Devi, and the title "Bar Raja" or chief king. Phuleswari minted coins in joint name of her and her husband where she used Persian legend, the first of its kind in Assam. Phuleswari was more under the influence of the Brahmins, particularly the Parvatiya Gosain, than the king had been. It is believed that instigated by this gosain and in her zeal for Sakta Hinduism she attempted to make Saktism the State religion. With this objective, she ordered the Vaishnava gosains to worship the goddessDurga. She then forbade the worship of other deities and personally supervised the act of desecration of the Sonarijan camp. Learning that the Sudra Mahantas were strong monotheists, she held a Durga puja in the capital Rangpur and forced Moamaria and several other gosains to offer oblations to the goddess and smeared sacrificial blood on their forehead. The Moamarias never forgave this insult to their spiritual leader, and half a century later, they broke out in open rebellion, which came to be known as Moamoria rebellion. Phuleswari died in 1731. The king then married her sister Deopadi, and made her the Bar Raja with the name Ambika. She died about 1738, and was succeeded by another wife named Enadari who took the name Sarbeswari on becoming Bar Raja. Siba Singha erected numerous temples and gave away land for support of Brahmins and temples with all the generosity of a new convert. Siva Singha was a great patron of literature and music. According to one Buranji he was himself the writer of a number of hymns. It was during his reign Sakta Hinduism became the predominant religion of Assam.
Siba Singha is said to have established such an elaborate system of espionage during his reign that he had accurate information of everything that was done or even spoken in all parts of his kingdom. During Siba Singha's reign, the chief public works were the construction of Dhai Ali and the tanks and temples at Gaurisagar, Sibsagar and Kalugaon. About south west of Sivasagar town by the side of National Highway-37, Bar Raja Phuleswari Konwari, the first wife of king Siba Sngha built three temples – Shiva dol, Vishnu dol and Devi dol on the bank of a big tank covering an area of including the banks. This big tank was dedicated in the name of 'Gauri' or 'Durga' for which it is known as Gaurisagar tank and the entire place is now known as Gaurisagar. She also had dug the Borpatra tank at Kalugaon beside the historical Jerenga Pathar in memory of her brother who happened to be a Borpatra Gohain during her regime. On the north-eastern side of that tank two temples, namely Bishnu Dol and Jagadhatri Dol were constructed on the bank of the tank named as Lakshmisagar Pukhuri. It was during his second wife Bar Raja Ambika's rule the Sibsagar tank, Bar Pukhuri, situated within the heart of Sivasagar town was dug. On its banks three temples were built in 1734 – the Sivadol, the Vishnudol and the Devidol. Many temples were also constructed by Swargadeo Siba Singha in Kamrup including Shripur Dewaloy, Ballilecha Shri ShriKali Dewaloy, Jaypal Than, Basudev Dewaloy all located in present Nalbari district. In Sualkuchi he built the Sidheswar Dewaloy, a Shiva temple. And in Dergoan he also constructed burhi goshani than. At Aswaklanta, North Guwahati on the bank of the river Brahmaputra in 1720 Siba Singha built two big temples dedicated to Lord Janardana and Lord Vishnu. Siba Singha had the land surveyed in Kamrup and Bakata. The register, or Pera Kagaz, based on this survey of Kamrup was still used at the time of British occupation. This contained a list of all occupied lands, except homestead with their areas, and particular of all rent free estates. It was recorded that in 1739 four Europeans, whose names appear to have been Bill, Godwin, Lister, and Mill, visited King Siba Singha at Rangpur. The king met them at the principal gate of the city where, it is said, they did him homage by falling prostrate at his feet.
Death
Siva Singha died in 1744 and Pramatta Singha, the second son of Rudra Singha ascended the throne.
