Etymologically, the word Seine comes from sequana, from Celtic quan ("winding"). Besides, a goddess Sequana exists, she was worshipped in Seine’s springs. People probably Christianized her through saint Seine’s character.
Another tradition said that Bacchus’ daughter, Seine, went in Gaul with Ceres. They were looking for Proserpine. They found here in Normandy. Ceres rewarded Seine by giving her lands and a special gift: to grow wheat.
But one day that she went about her business, on her land, Neptune saw her: she found her so pretty, and started to chase the lady. Seine ran away: oh, the god nearly reached her! But suddenly, miracle! She changed herself into water… the river Seine was born!