Augustine receives the credit (or blame, depending on your point of view) for the doctrine of original sin, that every human being by virtue of his birth is tainted and destined for damnation without baptism. He is currently a point of contention in Orthodox-Catholic relations, viewed by some as one who sent Western theology off into its eventual heresy.
But Augustine did not invent the doctrine. As he himself makes clear in Contra Julianum, he is following St. Cyprian and St. Ambrose, whom he quotes approving his own position. It seems clear that he is following doctrinal trends in Carthage and Italy. But what of the East? Augustine attempts to enlist St. John Chrysostom as a witness to his position.
This will be difficult, since St. John says "We baptize even infants, though they are not defiled with sin, in order that there may be given to them holiness, justice, adoption, inheritance, and the brotherhood of Christ, that they may be His members." (quoted from Homilia ad neophytos by Augustine in chapter 6, Contra Julianum.)
St. John says that "Christ wept because the Devil made mortal those who could have been immortal," (Homilia de Lazaro resuscitato.) Augustine enlists this as evidence that all have a guilt of sin. "Why do even infants die if they are not subject to the sin of that first man?" If death is the result of sin, then by what right are infants subject to death if they do not somehow share in the sin?
But this isn't quite what Augustine is saying. To say that infants suffer the effects of sin is not to say that they share in the guilt of sin. Given John Chrysostom's statement about baptism, it seems that he doesn't view original sin as constituting a guilt deserving eternal punishment, but as a damage to human nature. John means mortality as that which enters the world with the sin of Adam. This is sufficient for Augustine's argument with Julian, but not to establish unanimity on original sin between Augustine and John.
The difference is whether infants inherit sin or death from Adam. Augustine agrees that they inherit death, but reasons that they therefore inherit death because of guilt, and therefore need baptism not to share in the deserved condemnation of Adam.
But, it is clear that Augustine is not an innovator. He stands in a long tradition, and it would be improper to blame for what is a legitimate and ancient Christian teaching.
Perhaps more on this as I continue reading Contra Julianum.