But let us return to the heavenly city, and consider attentively its site, its form, its foundation, its gates, its walls, and its streets. Its site is upon the holy mountains, for so we read in the Psalm: "The foundations thereof are in the holy mountains" (Ps. 86). St. John agrees with this in the Apocalypse when he says: "And he took me up in spirit to a great and high mountain, and showed me the holy city" (Rev. 21). Now a city's site upon a mountain is wont to be serviceable both for the healthfulness of the air and for defense. But what mountains are higher than the heavens? And what mountain is exalted above all mountains, if not the heaven of heavens, of which David sang: "The heaven of heaven is the Lord's" (Ps. 113)? This is that mountain for which the same Prophet longed when he said: "Who shall ascend into the mountain of the Lord, or who shall stand in His holy place?" (Ps. 23). And it is from this mountain that he implored and awaited help, saying: "I have lifted up my eyes to the mountains, from whence help shall come to me" (Ps. 120). The site of the city of God, therefore, is so sublime that it utterly transcends everything that could in any way disturb the peace and quiet of the city. For it is too high for the dust and mire, the thorns and thistles, the bites and venom of the beasts of the earth to reach; too high also for the vapors and mists of the air, for hail and thunder, for fire and lightning to harm it; too high, finally, for those unclean and rapacious birds, which the Apostle in the Epistle to the Ephesians calls "the spirits of wickedness in the high places" (Eph. 6), to reach it in any way at all.
The form of the city of God is square, for so speaks St. John: "And the city lieth in a foursquare, and the length thereof is as great as the breadth" (Rev. 21). Now this signifies nothing else than the admirable and most perfect justice which reigns in that city, where nothing is unjust, nothing discordant, nothing distorted. So St. Augustine explains that verse of the Psalm, "Wonderful in equity" (Ps. 64)—that is, in justice. And surely it will be altogether wonderful to behold the inhabitants of that city, plainly innumerable and all endowed with the freest will, and yet to see that in not one of them, through all eternity, could anything distorted be found, whether in deed, in word, or in thought. Truly, then, that city is laid out as a square, so that its breadth does not exceed its length by even a little, nor its length its breadth. Yet that square figure may also signify that the breadth of the heavenly goods is equal to their length: for as their abundance will be infinite, so also will their duration be infinite. For breadth is wont to be applied to the abundance of a thing, and length to its duration. Thus in the first book of Kings the manifold wisdom of Solomon is called "a largeness of heart, as the sand that is on the seashore" (1 Kings 4); and in the ninetieth Psalm the duration of time is called "length of days." In the city of our God, therefore, there will be as much breadth as length, because there will be an immensity of goods together with everlasting duration. A little later St. John adds that the height of the city is also as great as its breadth, so that the city is squared on every side—because, namely, the goods of the heavenly city will be not only exceedingly many and everlasting, but also most noble and most exalted. Nor does it much matter that our own Vitruvius (Bk. 1, ch. 5) and Vegetius (Bk. 4, ch. 2) do not approve a square site for cities: for they speak of cities that fear enemies, whereas holy Scripture speaks of the city that "hath placed peace in her borders" (Ps. 147), and to which, by reason of its surpassing height, "evil cannot draw near," as the Prophet sang (Ps. 90).