Apart from those, Augustine is probably best known for his "Confessions", which is a personal account of his earlier life, and for "De civitate Dei" ("The City of God", consisting of 22 books), which he wrote to restore the confidence of his fellow Christians, which was badly shaken by the sack of Rome by the Visigoths in 410. His "On the Trinity", in which he developed what has become known as the 'psychological analogy' of the Trinity, is also considered to be among his masterpieces, and arguably of more doctrinal importance than the "Confessions" or the "City of God". He also wrote "On Free Choice of the Will" ("De libero arbitrio"), addressing why God gives humans free will that can be used for evil.