Augustine of Hippo

All that we indubitably know, from the authentic Scripture in the Hebrew and Christian traditions, is the fact that in the period before the flood there were many giants, all of whom belonged to the earthly city in human society, and that there were sons of God descended from Seth who abandoned their holiness and sank down into this city of men. There is nothing surprising in the fact that giants could be born from men like that. In any case, they were not all giants, even though there were more giants before the flood than in all subsequent ages. They served a divine purpose in that they reveal to anyone who is wise that mere bodily magnitude and might have no more value than bodily beauty.