Genesis 6:2-4

When the sons of God saw that these girls were beautiful, they married any of them they chose. The LORD said, “My Spirit will not remain in human beings forever, because they are flesh. They will live only 120 years.” The Nephilim were on the earth in those days and also later. That was when the sons of God had sexual relations with the daughters of human beings. These women gave birth to children, who became famous and were the mighty warriors of long ago.