Wikipedia
Vatsa
Vatsa ( Pali:Vaṁsa, Ardhamagadhi: Vaccha) was one of the solasa (sixteen) Mahajanapadas (great kingdoms) of Uttarapatha of ancient India mentioned in the Anguttara Nikaya it was situated in the Gangatic plain with Kausambi as its capital, now known as Kosam a small town in Uttar Pradesh. There is an archeological site known as Kosam Ruins in this town which is believed to be the Kausambi of Ancient India. Vatsa's geographical location was near the confluence of the Ganges and Yamuna rivers. Its capital was (present day Kosam, 35 miles southwest of Allahabad).