The capital of the Vatsas or Vamsas (J.iv.28; vi.236). In the time of the Buddha its king was Parantapa, and after him reigned his son Udena. (MA.ii.740f; DhA.i.164f). Kosambī was evidently a city of great importance at the time of the Buddha for we find Ananda mentioning it as one of the places suitable for the Buddha's Parinibbāna (D.ii.146,169). It was also the most important halt for traffic coming to Kosala and Magadha from the south and the west. (See, e.g., Vin.i.277).
The city was thirty leagues by river from Benares. (Thus we are told that the fish which swallowed Bakkula travelled thirty leagues through the Yamunā, from Kosambī to Benares, AA.i.170; PsA.491). The usual route from Rājagaha to Kosambī was up the river (this was the route taken by Ananda 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. (See Vin.ii.184f). In the Sutta Nipāta (vv.1010-13) the whole route is given from Mahissati to Rājagaha, passing through Kosambī, the halting-places mentioned being:
Near Kosambī, by the river, was Udena's park, the Udakavana, where Ananda and Pindola-Bhāradvāja preached to the women of Udena's palace on two different occasions (Vin.ii.290f; SNA.ii.514; J.iv.375). The Buddha is mentioned as having once stayed in the Simsapāvana in Kosambī (S.v.437). Mahā Kaccāna lived in a woodland near Kosambī after the holding of the First Council (PvA.141).
Already in the Buddha's time there were four establishments of the Order in Kosambī - the Kukkutārāma, the Ghositārāma, the Pāvārika-ambavana (these being given by three of the most eminent citizens of Kosambī, named respectively, Kukkuta, Ghosita and Pāvārika), 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. (Thomas, op. cit., 115, n.2, doubts the authenticity of the stories connected with the Buddha's visits to Kosambī, holding that these stories are of later invention).
The Buddha spent his ninth rainy season at Kosambī, and it was on his way there on this occasion that he made a detour to Kammāssadamma and was offered in marriage Māgandiyā, daughter of the brahmin Māgandiya. The circumstances are narrated in connection with the Māgandiya Sutta. Māgandiyā took the Buddha's refusal as an insult to herself, and, after her marriage to King Udena, tried in various ways to take revenge on the Buddha, and also on Udena's wife Sāmavatī, who had been the Buddha's follower. (DhA.i.199ff; iii.193ff; iv.1ff; Ud.vii.10).
A great schism 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 Bālakalonakāragāma and the Pācīnavamsadaya, 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 Sāvatthi, they asked his pardon and settled their dispute. (Vin.i.337-57; J.iii.486ff (cp.iii.211ff); DhA.i.44ff; SA.ii.222f; the story of the Buddha going into the forest is given in Ud.iv.5. and in S.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. But see UdA.248f, and SA.ii.222f).
The Commentaries give two reasons for the name Kosambī. The more favoured is (E.g., UdA.248; SNA.300; MA.i.535. Epic tradition ascribes the foundation of Kosambī to a Cedi prince, while the origin of the Vatsa people is traced to a king of Kāsī, see PHAI.83, 84) that the city was so called because it was founded in or near the site of the hermitage once occupied by the sage Kusumba (v.l. Kusumbha). Another explanation is (e.g., MA i.539; PsA.413) that large and stately margossa-trees (Kosammarukkhā) grew in great numbers in and around the city.
Bakkula was the son of a banker in Kosambī. (MA.ii.929; AA.i.170). In the Buddha's time there lived near the ferry at Kosambī a powerful Nāga-king, the reincarnation of a former ship's captain. The Nāga was converted by Sāgata, who thereby won great fame. (AA.i.179; but see J.i.360, where the incident is given as happening at Bhaddavatikā). Rujā was born in a banker's family in Kosambī (J.vi.237f). Citta-pandita was also born there (J.iv.392). A king, by name Kosambaka, once ruled there.
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; Mhv.iv.17).
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 Samyutta Nikāya (S.iv.179; but see AA.i.170; MA.ii.929; PsA.491, all of which indicate that the city was on the Yamunā) as being "Gangāya nadiyā tīre." This is either an error, or here the name Gangā refers not to the Ganges but to the Yamunī. Kosambī is identified with the two villages of Kosam on the Jumna, about ninety miles west of Allahabad. (CAGI.448f; Vincent Smith places it further south, J.R.A.S.1898, 503ff).