Simplify the following text for a Grade 6 native English-speaking person.
Original: Leonardo was born on April 15 , 1452 , `` at the third hour of the night '' in the Tuscan hill town of Vinci , in the lower valley of the Arno River in the territory of Florence .
Simplified: Leonardo was born on 15 April 1452 , in the Tuscan hill town of Vinci , in the valley of the Arno River .