Thanks guys - all really interesting and useful.
What I am interested in is Tertullian's allusion to God's prophecy to Rebekah in Gensis 25:23 - 'two nations are striving in your womb, and the elder shall serve the younger.' The ref occurs in 'Adversus Judaeos' and I think it's a way round the problem that Christianity was only a recent religion, certainly far newer than Judaism (something, indeed, that Julian II was to seize on a couple of centuries later). The problem is an especially embarrassing one for Tertullian, as he uses the argument from antiquity against both pagans and heretics in other works. The word 'maior' crops up in the Latin of the prophecy, so this brings in mos maiorum really nicely.
Thanks once again people - if anyone asks me why I think the internet is amazing, I will mention all the invaluable pointers you have given me.