Kasi was one of the most powerful of the sixteen mahajanapadas.
The name Kasi is the tribe who settled in the region around Varanasi where itself the capital was located. There is a belief that Varanasi got its name from the rivers that surround the city, namely Varuna and Asi. Kasi occupied a predominant position among the sixteen Mahajanapadas, before the rise of Buddha. A lot about Kasi is known from the tales of Jatakas, which are a voluminous body of myths and folklore revolving about previous births of the Buddha. This supremacy called for a long drawn conflict for mastery between other cities, like Kosala, Anga and Magadha with Kasi. Kasi was no doubt influential that is the reason why we get a mention of Kasi in the Vedic texts. Matsya Purana and Alberuni are the texts where we read Kasi as Kausika and Kaushika, others read it as Kasi.
The capital of this place is Varanasi. This is one of the foremost cities of India. It flourished in the reign of Brahmadatta. During this period, there was constant struggle between Kashi and Kosala