Texts furnish us with the names and description of a number of janapadas (political entities) in the early 1st millennium BC. In the central region, these were mainly kingdoms, while republics predominated in peripheral areas.
The sixteen Mahajanapadas ('great Janapadas') were the most important. The geopolitical map was constantly changing as the janapadas vied with each other for power.
The late 6th and 5th centuries saw the growth of four strong states, Avanti, Vatsa, Kosala and Magadha, at the expense of their weaker neighbours. Some cities were encircled with massive fortification walls around this time.
The great religious reformers, Buddha and Mahavira, were frequent visitors to Magadha's capital, Rajagriha, and to other cities of the mahajanadas. Several have later major religious complexes whose foundation can be traced back to this time, such as the Ghositarama at Kausambi.
Excavations have concentrated on the spectacular structures of these towns and much less is known about other aspects of life, although it is clear that commerce and industry flourished. Bimbisara of Magadha (reigned 543-491 BC), an accomplished statesman, married into the royal houses of Kosala and Vaisali and conquered Anga, giving Magadha access to profitable international seaborne trade.
His parricide son, Ajatashatru (reigned 491-459) annexed Kosala and, after a bloody sixteen-year war, conquered the Vrijji confederacy.
Magadha's geographical location gave it control of the central and lower Ganges plain, an area rich in agricultural lands and forests as well as iron ore; it profited also from the administrative efficiency of its rulers.
Under later rulers Magadha gained control of further territories to the south and west, making it the chief power in the subcontinent. The empire grew into a pan-Indian state under the Mauryans who reigned from 321 BC.
