| Conventional Long Name: | Kingdom of Kāśī |
| Common Name: | Kāśī |
| Today: | India |
| Era: | Iron Age India |
| Government Type: | Monarchy |
| Event End: | Conquered by Kaṃsa of Kosala |
| S1: | Kosala |
| Image Map Caption: | The Kāśī kingdom and the other Mahajanapadas in the Post Vedic Era |
| Capital: | Vārāṇasī |
| Common Languages: | Sanskrit Prakrit Pali |
| Religion: | Historical Vedic religion Jainism |
Kāśī (Pali: Kāsī) was an ancient kingdom of India whose existence is attested during the Iron Age. The inhabitants of the Kāśī were named the Kāsikas in Pāli and the Kāśeyas and Kāśikas in Sanskrit.
The Kāśī kingdom covered an area of 300 leagues. The northern border of Kasi which separated it from Kosala was the Sarpikā or Syandikā river, and the river Son formed its southern and eastern boundaries, separating it from Magadha in the east.
The capital of Kāśī was the city of Vārāṇasī, which was also named Ketumatī, Surundhana, Sudassana, Brahmavaddhana, Pupphavatī, Ramma, and Molinī.
The Kāśikas were first mentioned in the recension of the Atharvaveda.
The ruling clan of Kāśī appears to have been member of the Bhārata clan, and at one point Kāśī was ruled by one Dhṛtarāṣṭra (in Sanskrit) or Dhataraṭṭha (in Pāli) whom the calls a "Bharata prince." This Dhṛtarāṣṭra was defeated in battle by another Bharata king, named Śatānīka Sātrājita, after which the Kāśikas stopped kindling the sacred fire until the time of the .
However, the monarchs of Kāśī do not appear to have all belonged to the same dynasty, and the s frequently mention the extinction of dynasties of the Kāśika kings or the deposition of Kāśika princes and their replacement with members from other families regarded as being more competent, with some kings of Kāśī having Māgadhī or Vaideha origins and bearing the epithet of : although was a dynastic name, the Brahmadattas were not from the same dynasty, with the elected Brahmadatta of the having been a Māgadhī prince, the king of Kāśī in the and his son being both named Brahmadatta, the Kāśika king Udaya being called "Brahmadatta" in the, while the Brahmadattas of the and s were Vaidehas.
The Kāśikas were closely connected to the Kausalyas and the Vaidehas, and Jala Jātūkarṇya was the purohita of these three kingdoms during the reign of the Kāśika king Ajātaśatru, who was himself a contemporary of the famous Vaideha king Janaka and of Uddālaka Āruṇi's son Śvetaketu. Ajātaśatru appears in the s as engaging in philosophical discussions with Gārgya Bālāki, and the depicts Ajātaśatru as being jealous of Janaka's fame as a patron of learning. The calls this Ajātaśatru of Kāsī "Brahmadatta," implying that he was himself was a Brahmadatta.
The Śatapatha Brāhmaṇa mentions a king of Kāsī named Bhadrasena Ajātaśatrava, who was likely the son and successor of Ajātaśatru, and had been bewitched by Uddālaka Āruṇi.
Another king, named Janaka, who is not identical with the Vaideha king Janaka, is mentioned as ruling over Kāśī in the .
According to the, the legendary heroes Daśaratha and Rāma were kings of Kāśī, and not of Kosala as the Puranic tradition makes them out to be.
Vedic texts mention two other kings of Kāśī, one named Divodāsa, and his son or descendant, named Daivadāsi Pratardana.
During the 9th century BCE, the king of Kāsī was Aśvasena, the father of the 23rd Jain Tīrthaṅkara, Pārśvanātha.
By the later Iron Age, the kingdom of Kāśī had become one of the most powerful states of Iron Age South Asia, with several s describing the Kāsika capital of Vārāṇasī as being superior to the other cities and the kingdom's rulers as having imperial ambitions. According to these s, the kings of Kāśī sought the status of King of All Kings and of Lord of all South Asia . Vārāṇasī itself was twelve leagues in size, being much larger than the cities of Mithila and Indaprastha, which were both seven leagues in size, and the called Vārāṇasī the "chief city" of all South Asia.
According to the, a Kāśika king and his large army fought against it northern neighbour of Kosala and seized its capital of Srāvastī; the and the claim that the Kāśika king Brahmadatta had annexed Kosala after executing the Kauśalya king Dīghati; the mentions that Brahmadatta of Kāśī captured Kosala, killed its king, and carried of the chief Kauśalya queen to Vārāṇasī where he married her; according to the, the Kāśika king Manoja had sunjugated the kings of Kosala, Aṅga, and Magadha; the Mahābhārata claims Kāśī had destroyed the power of the Vitahavyas or of the Haihayas; and according to the, the kingdom of Aśmaka, in the Deccan, was under Kāśika suzerainty.
Kāśī itself, in turn, was coveted by the other kingdoms around it, and at one point, seven kings besieged Vārāṇasī in an attempt to conquer the territory of Kāśī, and the claims that the Kauśalya king had seized the kingdom of the king Mahāsīlava of Kāśī, while the kings Vanka and Dabbasena of Kosala were able to win suzerainty over Kāsī according to the and s.
Kāśī was finally conquered for good by Kosala under the latter's king Kaṃsa, shortly before the time of the Buddha, due to which Kaṃsa was nicknamed ("seizer of Vārāṇasī"}, and Kāśī was a full part of the kingdom of Kosala by the time of the Kauśalya king Mahākosala.
When Mahākosala's daughter Kosalādevi married the king Bimbisāra of Magadha, she was given as present a village in Kāśī which produced a revenue of a hundred thousand for bath and perfume money, while the rest of the former Kāśī kingdom remained part of the Kosala kingdom ruled by Mahākosala's son Pasenadi.
Following Bimbisāra's murder and the usurpation of the throne of Magadha by his son Ajātaśatru, Pasenadi revoked his rights over the village in Kāśī, after which a war between Kosala and Magadha ensued which ended when Pasenadi captured Ajātasatru, gave him in marriage his daughter Vajirā, to whom he gifted the village in Kāśī, and restored him to his throne.
Kāśī later became a part of the empire of Magadha when Ajātasattu defeated Pasenadi's own usurper son, Viḍūḍabha, and annexed Kosala.