Who started the practice of erecting gravestones?

[Epictetus]

I took it to mean that the stone was found in a tomb or mausoleum of sorts? I assumed that was why they think he was cremated - they found ashes. (Or the other option would be that the stone says he was cremated, I suppose.) That Italian Iron Age cemetary I mentioned previously included full-body inhumations as well as cremated remains buried in those urns shaped as huts.