Ancient Rome is one of the most consistently popular subjects in history. School curricula, university courses, documentaries, podcasts, games, novels, and an enormous general readership that never seems to diminish.
The .org is exactly right for it. Classical studies live in universities, museums, learned societies, and archaeological institutes, all of which use that extension. A teaching resource, an archive, a society, a museum project, or an educational publisher would all look native at this address.
The content opportunity is genuine. Roman history is taught everywhere and the online resources for it are a mix of old university pages and thin content farms. Something authoritative, well illustrated, and properly structured would find an audience immediately, particularly among students and teachers.
Two words, exact match, no hyphen, no ambiguity, and a subject with two thousand years of accumulated material and no risk whatsoever of becoming irrelevant.
Available now. Enquiries welcome.