In his superb introduction to the New City Press edition of  Augustine’s de Trinitate ( Trinity, The (Works of Saint Augustine A Translation for the 21st Century) ), Edmund Hill offers a chiastic outline of the treatise:

1. Introduction, 1

2. Divine missions: exegetical, 2-4

3. Trinitarian language: philosophical, 5-7

4. Modo interiore , 8

3’. Psychological analogies: philosophical, 9-11

2’. Disorder and redemption of image: exegetical, 12-14

1’. Conclusion, 15