Referring to progressively more distance ancestors, I would list my
- Pater (father)
- Avus (grandfather)
After this point, it gets a bit shaky. This, for example, gives past ancestors as
- Proavus (great-grandfather)
- Abavus (great-great-grandfather)
- Atavus (great-great-great-grandfather)
- Tritavus (great-great-great-great-grandfather)
See also here.
I don't know how far back this system went on — I have yet to find anything further — although it seems somewhat absurd that someone should need to refer to someone this distantly related.
If I were to literally translate "grand" in this usage, I would end up with some form of magnus, which could then be applied as successive prefixes. However, I doubt that this has actually been used; it seems like a misrepresentation. The book I cited also gave pro- as meaning
'add one generation away from ego.'
This might then mean that my atavus could also be called my pro-pro-proavus. However, pro- can also be used to indicate steps in future generations — and may in fact have been used more commonly in this way.
What system was most commonly used in Classical Latin — the specific naming system, applicable to at least six generations back in time, the pro- system, which could apparently be used for an arbitrary number of generations (which I'm slightly more interested in here), or something completely different?