Another fine definitional problem you have got us into....!
Are "busty" Apsaras in Angkor Wat "erotic" and what about naked bathers in Quseir Amra (or even, dare one suggest it, the statue of David in Florence!)? It depends what "turns one on" I suppose. Should our definition of "erotic" emphasise the depiction's intention or its activity? My inclination is to emphasise the activity since the intention depends too much on what is regarded as erotic in the receiving culture. So that would allow in the bordello scenes in Pompeii, the Hindu depictions and (possibly??) any Phallic depictions - but presumably not simply Hindu Lingams? We must require a degree of realism in the depiction of the member surely, otherwise it is just a representation of "fertility"!
I feel like our one-time censor the Lord Chancellor who used to require a ruler and a set square to help determine whether something was pornographic or not!!