Folk tales say the following about the birth of Nizhny Novgorod:
A white king sailed along the Volga River with his retinue and stopped at the Dyatlovy Mountains, where he saw Mordovians praying to their pagan gods. And the white king ordered his servants to give the Mordovian elders each a barrel of gold and silver. And so they gratefully sent the king dishes full of bread, honey and salt. However, the Mordovian ambassadors, young men, got tired along the way and ate all the bread, salt and honey. To hide the fact this had happened, they filled the empty dishes with soil and sand, and presented them like that to the white king.
The king gratefully accepted the gifts and thanked the Lord, saying, "Thank you for delivering Mordovian land to my hands," because he'd decided that the Mordovians gave him their territory. And the king went further along the river, scattering sand and earth: wherever he left a handful, a city was built, where he left a pinch, a settlement would be established.
So the Russian people appeared in Mordovian lands, and at the confluence of the Oka and the Volga a "new city" appeared - Novgorod, which later was called Nizhny Novgorod. This was either because the city was in the lowlands with respect to its "older brother" Novgorod the Great, founded in the middle of the IX century in the north-west of Russia, or because it was down river from another "old city."