Forasmuch as each man is a part of the human race, and human nature is something social, and hath for a great and natural good, the power also of friendship; on this account God willed to create all men out of one, in order that they might be held in their society not only by likeness of kind, but also by bond of kindred. Therefore the first natural bond of human society is man and wife. Nor did God create these each by himself, and join them together as alien by birth: but He created the one out of the other, setting a sign also of the power of the union in the side, whence she was drawn, was formed. For they are joined one to another side by side, who walk together, and look together whither they walk. Then follows the connexion of fellowship in children, which is the one alone worthy fruit, not of the union of male and female, but of the sexual intercourse. For it were possible that there should exist in either sex, even without such intercourse, a certain friendly and true union of the one ruling, and the other obeying.
S. Augustine of Hippo, De bono coniug. 1.1