What was Augustine's teaching on Original Sin?

Augustine taught that in a post-lapsarian world the sin of Adam was still causing effects. Augustine believed that all humans today were seminally present in Adam and consequently through him original sin has been passed onto everybody. Consequently we see that for Augustine sin is an ontological condition of human existence and nobody is morally good in an absolute sense. This original sin was described by Augustine as a "double death". The first death being Adam's biting of the apple in the Garden of Eden and the second death being the moral state of every human as a result. Augustine also strongly focused on the transmission of this sin, how all humans are born into it and therefore are "tainted" by concupiscence. Humans in this paradigm do not voluntarily choose sin but instead are prone to it.