ancient kingdom of India, situated in what is now west-central Bihar state, in northeastern India. It was the nucleus of several larger kingdoms or empires between the 6th century BC and the 8th century AD.

The early importance of Magadha may be explained by its strategic position in the Ganges River valley, enabling it to control communication and trade on the river. The river further provided a link between Magadha and the rich ports in the Ganges delta.

Under King Bimbisara (reigned c. 543-c. 491 BC) of the Haryanka line, the kingdom of Anga (eastern Bihar) was added to Magadha. Kosala was annexed later. The supremacy of Magadha continued under the Nanda (4th century BC) and Mauryan (4th-2nd century BC) dynasties; under the Mauryan dynasty the empire included almost the entire subcontinent of India. The early centuries AD saw the decline of Magadha, but the rise of the Gupta dynasty in the 4th century brought it once more to a position of preeminence. Not only did these imperial dynasties begin by establishing their power in Magadha but in each case Pataliputra (adjacent to modern Patna) was the imperial capital, thus adding to the prestige of Magadha.

Lively accounts of Pataliputra and Magadha are available in the Indica of Megasthenes (c. 300 BC) and in travel diaries of the Chinese Buddhist pilgrims Fa-hsien and Hsuan-tsang (4th-5th and 7th centuries AD). Many sites in Magadha were sacred to Buddhism. Toward the close of the 12th century, Magadha was conquered by the Muslims.