Explanation:

Saraswati River refers to a river,  that was a distributary of  the Bhagirathi and is now no more there but was active  till  around the 16th century AD. The course and condition of the Saraswati has played an important role in the development and decline of river port towns in Bengal. Initially, the major port town was Tamralipta, after the decline of which Saptagram rose and declined, and finally Kolkata came up.