The constructive half of the work, books eleven to twenty two, narrates all of history as the story of two cities. They are founded, Augustine says, by two loves: the earthly city by love of self reaching contempt of God, the heavenly by love of God reaching contempt of self. The cities are not church and state, and the distinction is the book's subtlest point. Membership is decided by the orientation of the heart, so the institutional church contains citizens of the earthly city and the earthly city's institutions contain pilgrims of the heavenly one; the two populations are inseparably mingled until the last judgment sorts them.
Augustine traces both lines from the angels' fall and Cain and Abel through Israel and the nations to the age of the church, which he refuses to read as history's triumphant final act, coining instead the sober image of the saeculum, the overlapping time in which both cities share the same earthly peace, use the same goods, and suffer the same losses. The closing books turn to the ends: judgment, punishment and the eternal sabbath of the saints, with the resurrection of the body defended at length against Platonist disdain. Peace is the thread that binds the argument, defined as the tranquillity of order, and the earthly city's peace, real but provisional, is honoured exactly as far as it goes.