From Henry Chadwick's introduction to Augustine's Confessions:

The Confessions took some of its impetus from a wish to answer critics both inside and outside of the Catholic community. The exploitation of the case against Augustine by the Donatists helps to explain the fact, at first sight surprising, that the work makes not even the most oblique reference to the existence of Donatists, though every day of Augustine's life as a bishop was certainly beset by problems arising out of the schism with all its rancour and periodic violence. No reader of the work would ever guess that Augustine was now presiding over a minority community in Hippo, under the necessity of fighting for its life against a militant majority.