While neither the ancient Greeks nor Romans had a specific term to describe what we call rape (coerced/non-consensual sexual intercourse), it would be easy to show that the concept was well understood throughout Antiquity. The theme of sexual violence and non-consensual sex is extremely common in mythology as well as surviving law codes as far back as the Hittites and Babylonians. Some ancient peoples may have lacked a word for rape, but they were clearly very preoccupied with it.

But that is not exactly what you're asking here. You're already aware that many of these laws, and a number of the myths, frame the rape of women in a way that seems alien to our modern understanding of the crime. In Athenian law, there was hardly any distinction between rape and adultery (i.e. willing participation in an extramarital affair). A woman's consent or lack thereof was not considered a significant part of the matter. Indeed, survivors would always face blame and punishment even when there was no doubt that they had been forced. Girls who had survived sexual violence were socially unacceptable as marriage partners; married women who had been raped were forced to divorce their husbands. Rape and adultery were again confused in stereotypical responses to survivors: it would be assumed that they were promiscuous and immodest and likely to end up in the same place again. The stigma associated with being a survivor of rape - which also reflected badly on the survivor's entire household and family - was such that many women chose suicide rather than suffer sexual violence or chose to take their own lives after they had been raped.

The reason for this notion of sexual violence as a pollution or exposure of the corrupt nature of the survivor, resulting in their legal and social punishment, was patriarchy. There was little to no distinction between rape and adultery because the crime was ultimately the same: the violation of a man's "property" (a woman in his household) and the purity of his bloodline. When an unmarried girl was raped, she lost the "purity" that made her an appealing bride and a potential connection between families. When a married woman was raped, she lost the ability to guarantee that the children she bore her husband were his own. These male anxieties are reflected in laws that never show the slightest concern with women's health or trauma, and that always assume something is wrong with the victim as well as the perpetrator. A woman who had sex outside of marriage was "polluted" whether she gave her consent or not.

This is essential context for understanding the discussion in Augustine's City of God. He was writing in a world where all (freeborn, citizen) women who had been raped were considered to have lost something essential to their social status and dignity. Augustine disputes this on the grounds of his Christian beliefs. Now, admittedly I am no theologist, but the author's own words seem to reflect his ideas pretty well. He argues that what affects the body does not change the nature of the soul, which contains the true moral standing of a person:

The virtue which makes the life good has its throne in the soul, and thence rules the members of the body, which becomes holy in virtue of the holiness of the will; and while the will remains firm and unshaken, nothing that another person does with the body, or upon the body, is any fault of the person who suffers it, so long as he cannot escape it without sin.

It follows that any victim of sexual violence is truly blameless as long as they remained defiant in their soul. He goes on to argue that they would be guilty of murder if they took their own lives after their ordeal, since they would have killed an innocent person.

The reason he needed to argue this at such length should now be obvious: it went against the prevailing and legally enshrined notion of the nature of rape survivors, and it directly contradicted the common and morally endorsed resolution of sexual assault narratives (namely, women taking their own lives to avoid a life of shame). But this does not mean that Augustine's view of rape was a radical innovation. Augustine clearly invokes the story of Lucretia to make this precise point: that his view is not really so alien to those who may instinctively resist it.

The story is recounted in Livy 1.57-58. A noble named Sextus Tarquinius gains entrance to Lucretia's house while her husband Collatinus is away, and threatens her at swordpoint. She defies him even in the face of death. He goes a step further, threatening to kill her and his male slave, and then to strip him naked and lay him next to her in bed, if she does not comply. The fact that this threat does compel her is significant: it is assumed Lucretia would find it unbearable to be thought (posthumously) to have been in an adulterous relationship with her social inferior. Instead she yields to Tarquinius. (Consent given under threat of violence or disgrace is not consent.) After Tarquinius leaves, Lucretia calls on her husband and his close confidants to hear her. The scene in Livy shows how Lucretia has internalised the common attitude to rape survivors:

To her husband's question, "Is all well?", she replied, "Far from it; for what can be well with a woman when she has lost her honour?"

But even in Livy's account (written some 400 years before Augustine), Lucretia already makes a distinction between what her body has endured and what she identifies as her own will: "My body only has been violated; my heart is guiltless." Not only that, but her husband and his friends try to console her by reinforcing this view:

They seek to comfort her, sick at heart as she is, by diverting the blame from her who was forced to the doer of the wrong. They tell her it is the mind that sins, not the body; and that where purpose has been wanting there is no guilt.

The reason she gives for nevertheless ending her life reflects the role often played by ancient elite women in policing the oppressive and misogynist values of their society. She claims that "not in time to come shall ever unchaste woman live through the example of Lucretia" - that is, she refuses to live on and set a precedent for other women who were guilty of the "crime" of adultery.

What the story of Lucretia shows is that the notion of rape as a mark against the survivor, as an act corrupting both perpetrator and victim, can in fact coexist with the understanding that the victim is not to blame. This is much more important for Augustine than for earlier ancient authors because of his Christian belief that the soul is the true essence of a person that will be judged before God. But the idea itself was not new at the time, and would undoubtedly have been raised in many earlier instances of sexual violence by those who sought to treat and console survivors.