A medieval town that gets its name from a tank that was excavated by the Ahom King Siva Singha in 1734 A.D. The Ahom Monarchs undertook excavation of extensive tanks and these became popularly known as sagar or 'sea;' and the impact of such a tank on the minds of the common people is so great that the locality around the tanks became known by the name of the tank itself. Another notable feature is that most of the tanks excavated still maintain a water-level much higher than the topography of the surrounding land.
Three temples were built on its south bank, a Shiva temple, a Devi Temple and a Vishnu temple. The Shiva temple being the main temple. Reaching a height of 40 metres, the Shiva temple is the tallest monument of the Ahom period.
Ahom Kings changed their capitals from place to place either due to military or political uncertainties or due to the havoc of floods. King Rudra Singha founded Rangpur in the year 1698. This old capital of the Ahom Kingdom, which possesses the largest secular buildings built by the Ahoms, lasted for 200 years. It is now a part of Sibsagar town.

The Talatal Ghar, built by Rudra Singha, and enlarged by Rajeswar Singha (1751-1769), was not the residential building of the royalty but a house for the functioning of the government. It is here the king gave judgment, received his vassals and other dignitaries. The place of royal residence was just north of this complex, which was traditionally done in timber and thatch, a reason why it does not survive today. The chief architect was Ghanashyam, who was brought from Koch Behar.
The two storied Rang-ghar at Rangpur was built by King Pramatta Singha in 1746. It constituted a royal pavilion used for witnessing outdoor sports such as wrestling, elephant fights, buffalo fights, falconry, etc. The architecture was perhaps imitated from the Namghars.
Other places of interest in Sibsagar include the Garhgaon Kareng Ghar - the Ahom King Suuklengmung built the palace when he shifted the capital from Cheregaon (north of Sibsagar town on the banks of the Dikhow River) in 1539.
The palace was built in 1540, but was destroyed and at the very site on which the old palace existed, a new palace was built by King Rajeswar Sinha I 1762 AD. The structure was built in bricks and is almost square in plan and consists of four stories.