The capital of the Vatsas or Vaṃsas. In the time of the Buddha its king was Parantapa, and after him reigned his son Udena. Kosambī was evidently a city of great importance at the time of the Buddha for we find Ānanda mentioning it as one of the places suitable for the Buddha’s Parinibbāna.DN.ii.146 DN.ii.169 It was also the most important halt for traffic coming to Kosala and Māgadha from the south and the west. Vin.i.277

The usual route from Rājagaha to Kosambī was up the river. This was the route taken by Ānanda when he went with five hundred others to inflict the higher punishment on Channa, Vin.ii.290 though there seems to have been a land route passing through Anupiya and Kosambī to Rājagaha. Vin.ii.184f. In the Sutta Nipāta Snp.1010–1013 the whole route is given from Mahissati to Rājagaha, passing through Kosambī, the halting-places mentioned being Ujjeni, Gonaddha, Vedisa, Vanasavhya, Kosambī, Sāketa, Sāvatthī, Setavyā, Kapilavatthu, Kusinārā, Pāvā, Bhoganagara and Vesāli.

Near Kosambī, by the river, was Udena’s park, the Udakavana, where Ānanda and Piṇḍola-Bhāradvāja preached to the women of Udena’s palace on two different occasions. Vin.ii.290f. The Buddha is mentioned as having once stayed in the Siṃsapāvana in Kosambī. SN.v.437

Already in the Buddha’s time there were four establishments of the Order in Kosambī—the Kukkuṭārāma, the Ghositārāma, the Pāvārika-ambavana, and the Badarikārāma. The Buddha visited Kosambī on several occasions, stopping at one or other of these residences, and several discourses delivered during these visits are recorded in the books.

A great division once arose among the monks in Kosambī. Some monks charged one of their colleagues with having committed an offence, but he refused to acknowledge the charge and, being himself learned in the Vinaya, argued his case and pleaded that the charge be dismissed. The rules were complicated; on the one hand, the monk had broken a rule and was treated as an offender, but on the other, he should not have been so treated if he could not see that he had done wrong. The monk was eventually excommunicated, and this brought about a great dissension. When the matter was reported to the Buddha, he admonished the partisans of both sides and urged them to give up their differences, but they paid no heed, and even blows were exchanged. The people of Kosambī, becoming angry at the monks’ behaviour, the quarrel grew apace. The Buddha once more counselled concord, relating to the monks the story of King Dīghiti of Kosala, but his efforts at reconciliation were of no avail, one of the monks actually asking him to leave them to settle their differences without his interference. In disgust the Buddha left Kosambī and, journeying through Bālakaloṇakāragāma and the Pācīnavaṃsadāya, retired alone to keep retreat in the Pārileyyaka forest. In the meantime the monks of both parties repented, partly owing to the pressure exerted by their lay followers in Kosambī, and, coming to the Buddha at Sāvatthī, they asked his pardon and settled their dispute. Vin.i.337–357 The story of the Buddha going into the forest is given in the Udāna Ud.iv.5 and in the Saṃyutta, SN.iii.94 but the reason given in these texts is that he found Kosambī uncomfortable owing to the vast number of monks, lay people and heretics.

During the time of the Vajjian heresy, when the Vajjian monks of Vesāli wished to excommunicate Yasa Kākandakaputta, he went by air to Kosambī, and from there sent messengers to the orthodox monks in the different centres. Vin.ii.298

It was at Kosambī that the Buddha promulgated a rule forbidding the use of intoxicants by monks. Vin.ii.307

Kosambī is mentioned in the Saṃyutta Nikāya SN.iv.179 as being on the Ganges, but here as elsewhere this simply means on a great river, in this case the Yamuna.