Little Mary: I find in my history book there is always such number (1451--1560) after the name Christopher Columbus. Would you please explain why, sir?

• 小玛丽：我在历史书中发现，克里斯托。哥伦布这个名字后老是有(1451-1560)着几个数字，老师，请您给解释一下好吗？