Answer:
Some of our great cities are on the banks of rivers.
One of the oldest was Indraprastha, which was somewhere near Delhi.
Banaras or Kashi is also very old, perhaps one of the oldest existing cities in the world.
Allahabad, Vijaywada and Patna and many others, are also on the banks of rivers.
Though most of these are not very old, Allahabad or Prayag and Patna or Pataliputra, as it used to be called, are pretty old.
Prayag is a place of sacrifice.
The Mughal Akbar renamed Prayag as Allahabad.
Allahabad means "the City of" God.
The name Pataliputra is believed to have come from the Sanskrit word tell.