This district was famous as second Kashi during 11th to 13th centuries. In the 9th century B.C., the Brahmadutt dynasty was subdivided by Nagas. Kushan and Nagas also held supremacy over this region before the advent of the Gupta period. After the death of Harshvardhan in the latter half of the 7th century, it remained under the control of the Gurjara-Pratihars till 1025 before they were driven out by Mahmud of Ghazni. This area was under the administration of various Governors of Mughal emperors. Some of the forts such as Agori Fort were under the control of Madan Shah. During the 18th century, the district came under the control of the Narayan rulers of Benares State, who built or occupied several fortresses in the district. In the decade after 1775, the British took over administrative control of most of the territory of the rajas of Benares. The British district of Mirzapur included present-day Mirzapur and Sonbhadra districts, with all of present-day Sonbhadra district included in Robertsganj tehsil. On 4 March 1989, Sonbhadra district was divided from Mirzapur district. The heroine of Famous Novel Chandrakanta written by Devaki Nandan Khatri was the princess of Vijaygarh and the daughter of king Jay Singh. The northern part of the district lies on a plateau of the Vindhya Range, and is drained by tributaries of the Ganges including the Belan and Karmanasha rivers. South of the steep escarpment of the Kaimur Range is the valley of the Son River, which flows through the district from west to east. The southern portion of the district is hilly, interspersed with fertile stream valleys. The Rihand River, which rises to the south in the highlands of Surguja district of Chhattisgarh, flows north to join the Son in the center of the district. The Govind Ballabh Pant Sagar, a reservoir on the Rihand, lies partly in the district and partly in Madhya Pradesh. East of the Rihand, the Kanhar River, which originates in Chhattisgarh, flows north to join the Son. The district has historic, cultural, and ecological affinities with the Bagelkhand region. Robertsganj is the district headquarters. Sonbhadra has a relatively subtropical climate with high variation between summer and winter temperatures.