There are several passages in the Old Testament that speak of the Rephaim (or Rephaites), and the context describes them as giants. The name of these people literally means “terrible ones.”
The Hebrew word Rephaim has two distinct meanings: first, in poetic literature it refers to departed spirits whose dwelling place was Sheol. It is a figurative description of the dead, similar to our concept of a ghost. The second meaning of Rephaim is “a mighty people with tall stature who lived in Canaan.” The word doesn’t seem to be ethno-centric like “Jew” or “Egyptian” but is more of a descriptive term.
The first reference to the Rephaim is Genesis 14, when the Rephaim, Zuzim and Emim people were defeated in a battle with Kedorlaomer and his allies.
“And in the fourteenth year came Chedorlaomer, and the kings that were with him, and smote the Rephaims in Ashteroth Karnaim, and the Zuzims in Ham, and the Emins in Shaveh Kiriathaim.” Genesis 14:5
When the Israelites first approached the Promised Land after the Exodus from Egypt, they were afraid to enter the land because it was filled with “giants” (the word used in Numbers 13:33 for giants is Nephilim), the sons of Anak.
Giants were widely scattered through Canaan, but were known by different local names, including Rephaim, Zuzim, Emim, and Anakim. Deuteronomy 2 says the Rephaim were strong and tall, like the Anakites.
“That also was accounted a land of giants: giants dwelt therein in old time; and the Ammonites call them Zamzummims; A people great, and many, and tall, as the Anakims; but the Lord destroyed them before them; and they succeeded them, and dwelt in their stead:”Deuteronomy 2:20–21
Og, king of Bashan, was described as the last of the Rephaim in his land Deuteronomy 3, measures his bed at thirteen feet long and six feet wide.
“For only Og king of Bashan remained of the remnant of giants; behold his bedstead was a bedstead of iron; is it not in Rabbath of the children of Ammon? nine cubits was the length thereof, and four cubits the breadth of it, after the cubit of a man.” Deuteronomy 3:11
The Septuagint uses the Greek words gigas and titanes (the source of the English titan) to translate these and other verses, so the ancient Jews considered them to be giants. They are described generally as being between 12 and 18 feet tall and are called “mighty men.” The Egyptians wrote about giants who lived in the land of Canaan, and the folklore of other nations is full of such references. The people of the ancient world accepted the presence of giants as a fact of history, and the Bible presents them as enemies who were destroyed either by the judgment of God or in battle with men.
So where did these giants come from? One theory, based on Genesis 6:1–4, is that fallen angels (the sons of God) had sexual relations with women, resulting in the birth of giants. This is remarkably similar to Greek and Roman myths about demi-gods, but the theory has some theological and biological obstacles. Another theory, also based on Genesis 6, is that the fallen angels, having knowledge of human genetics, indwelt certain men and women who would have the right traits to produce a race of giants and induced them to cohabit with each other. A third theory is that the giants were simply the result of normal genetic variability within a society. Whatever the origin of the Rephaim, it is certain that a race of “giants”—strong, tall people—did exist at one time, and many cultures had dealings with them.
Even today, there are people who grow to extreme sizes, whether through genetic disorders like gigantism or through normal heredity. In the last 10 years, more giant bones have been found around the world that have been authenticated as human, with sizes greater than 30 feet. There are a number of Supreme Court cases between National Geographic and the Smithsonian over the disclosure of these giant remains.