Genesis 6:1-4

When the human race had spread all over the world, and daughters were being born, some of the heavenly beings saw that these young women were beautiful, so they took the ones they liked. Then the LORD said, “I will not allow people to live for ever; they are mortal. From now on they will live no longer than 120 years.” In those days, and even later, there were giants on the earth who were descendants of human women and the heavenly beings. They were the great heroes and famous men of long ago.