Genesis 6:4

Giants. It is likely the generality of men before the flood were of a gigantic stature, in comparison with what men now are. But these here spoken of, are called giants, as being not only tall in stature, but violent and savage in their dispositions, and mere monsters of cruelty and lust. (Challoner) --- Yet we need not imagine, that they were such as the poets describe, tearing up mountains, and hurling them against heaven. Being offspring of men, who had lived hitherto with great temperance, but now gave full scope to their passions, and the love of the fair daughters whom they chose, we need not wonder that they should be amazingly strong and violent. Nephilim, rushing on, as Ag. translates. That there have been giants of an unusual size, all historians testify. Og, Goliah[Goliath], &c. are mentioned in Scripture, and the sons of Enac are represented as much above the common size, as the Hebrews were greater than grasshoppers, Numbers xiii. 34. If we should suppose they were four or five times our size, would that be more wonderful that they should live nine or ten times as long as we do? See St. Augustine, City of God xv. 9, 23; Calmet's Dissert. &c. Delrio affirms, that in 1572 he saw at Rouen, a native of Piedmont, above nine feet high. (Haydock) --- Of old. The corruption of morals had commenced many ages ago, and some of the sons of Seth had given way to their lusts; so that we are not to suppose, that these giants were all born within a hundred years of the flood, as some might suppose from their being mentioned here, after specifying the age of Noe, chap. v. 31. (Haydock)