Vatsa (Pali:Vaṁsa, Ardhamagadhi: Vaccha) was one of the solasa (sixteen) Mahajanapadas (great kingdoms) of Uttarapatha of ancient India mentioned in the Anguttara Nikaya.
Vatsa's geographical location was near the confluence of the Ganges and Yamuna rivers. Its capital was Kauśāmbī (present day Kosam, 35 miles southwest of Allahabad).
Read more about Vatsa: The Early Period, Śatānīka II, Parantapa, Udayana, Later Developments, The Vatsa Vow