I'm considering an alternative history of the Earth were in the last century of the Western Roman Empire, a large group of christian settlers, about 1.000, from a mix of the nestorian and the manichean sects, arrived to South Australia from India.
These settlers soon lost every contact with the other cultures of the Old World and in few centuries created a little but extremely prosperous empire of confederated state-cities along the shores of South and South-East Australia. Their political form was a sort of elective monarchy-theochracy where every city had a bishop-king and all of them elected a Pope-Imperator.
I have a long list of questions to ask for improving the plausibility of this history and this empire, but the first that waits for your advice is this:
1.- What are the most plausible relations of these late-roman-early-mediaeval christians with the australian aboriginal population?
Is important to know some things about these settlers:
1.- The religion and moral of this para-manichaean sect abhorres slavery and war. They will barter or beg every thing they take, even land. Their religious values also make their population increase extremely low. They use to be extremelly honest in trade and politics.
2.- Their "science" and technology is equal to the late roman, but there were only basic artisans and humble peasants between the first setlers. They had no philosophers, no librarians, no warriors, no architects. They know the principles of basic roman buildings: bricks, teals, archs, water supply, but they couldn't build a huge domed Pantheon.
3.- Some of them can read and write, but their culture is proper from the lowest classes. They haven't kept with them most of the classical greek and latin writings. The first settlers have a large degree of familiarity with roman religion and mythology, but they reject it.
4.- They are not racist (if such ideology was posible in late Antiquity) but they are not proselitist. They consider that a man has to know extremely well their religion before being accepted into his group. They will teach some basic concepts of their religion to the native people if they are begged to, but they will not go very far if they are not pressed.
5.- They believe that true Salvation is impossible without a harsh ascetic and philosophical effort to achieve perfection. When a man dies and has done enough merits, they believe, he reencarnates in a child belonging to a "more saint" and socially superior family where he will have more chances to improve himself. They marry and have childs, but sex is "imperfect" and very large families are shameful. They will not practice marriage or sex with natives. If there are children from some "sins" comitted with natives, these persons will be feeded and nurtured and treated kindly, but they will never be accepted in the "saint" classes.
I think that the result of this interaction may be some kind of feudalism where the economically and technically more advanced manichaean-christians will be the upper castes, but I beg for your opinions.