The Nephilim were on the earth in those days, as well as later, when the sons of God slept with the daughters of other humans and had children by them. These children were famous long ago.
Then they said, “Let’s build a city for ourselves and a tower with its top in the sky. Let’s make a name for ourselves so that we won’t become scattered all over the face of the earth.”
(Of the Rephaim only King Og of Bashan was left. His bed was made of iron and was more than 13 feet long and 6 feet wide. It is still in the Ammonite city of Rabbah.)