Possible Clues:

• Cato's 1,501
• Century opening
• 1501 in Roma
• Year in an Amerigo Vespucci voyage
• Year Vespucci sailed to the New World
• 1,501, another way
• Year in Ivan the Great's rule
• Year Michelangelo began 'David'
• When Michelangelo started ''David''
• Year in which Michelangelo began work on "David"