Answer:
Easy, River Ganges and the Son River.
Step-by-step explanation:
Moreover, these two Rivers also represents the boundary of the original kingdom.
Magadha was the most powerful nation at the time and was home to 2 of largest and the greatest empires in Indian subcontinent. Namely, Gupta Empire and the Mauryan Empire. Emperor Dharma Ashoka is considered the greatest ruler of them all.
Today, the region of Magadha belongs to Bangladesh and the Indian state of West Bengal and Bihar.