Kingdom of Kashi
The Kingdomin of Kashi was an ancient Indian kingdom located in the region around its capital Varanasi, the latter bounded by the Varuna and Asi rivers in the north and south and named after them. It was one of the sixteen Mahajanapadas, great states that emerged in northern India at the start of the 6th century BCE. The kingdom of Kashi was bigger than Varanasi. Its easternmost border was the Son River, which was also the western border of erstwhile Magadh. It would have covered much of the area of Eastern UP centered around today's Varanasi  and the contemporary southwestern part of Bihar that was Arrah (Shahabad) district. Today this area comprises Bhojpur, Rohtas, Kaimur and Buxar districts. Technically, the territory of Kashi today would dominated by people of the Bhojpuri language and culture. Kashi Mahajanpad would still be larger than what is covered within the Panch Krosh Kashi, as defined in the "Puranas". King Kasha (Ayu's great grandson and Kshatravriddha's grandson) founded the rule of Chandravamsha in Varanasi and rebuilt or expanded the city. So on the name of King Kasha Varanasi came to be known as 'Kashi'. The Jataka tales indicate Varanasi  was one of the richest cities in India, known for its prosperity and opulence. These stories tell of a prolonged rivalry between the neighboring kingdoms of Kashi and Kosala, with also some occasional conflict with Anga and Magadha. Kashi once was one of the most powerful states in north India. Although King Brihadratha of Kashi conquered Kosala, during Buddha's time Kashi was incorporated into Kosala by King Kansa. The Kashi, along with the Kosala and Videhan, are peoples mentioned in Vedic texts and appear to have been closely allied. Siddartha Gautama first started preaching Buddhism in Kashi territory. At  the time of Chanakya, Kashi was still the center of Vedic and secular education par excellence, despite the prominence of Magadh. It was known more for military prowess. While Varanasi came under Buddhist influence, Shahabad remained a dominion of Hindu Shaivite culture, as reported by Chinese pilgrims.