WI: Roman Expansion down the Nile

[Saepe Fidelis]

So there are obvious reason why Rome didn't advance down the Nile: political instability, a monolithic bureaucracy, and the fact that by the time the legions got that far the Empire's foreign policy was generally defensive. Furthermore, the Nile cataracts made any upriver transportation difficult.

However, what if Roman influence, cultural or otherwise, spread down the Nile to Sub-Saharan Aarica? The Nubian kingdoms had had contact with Egypt for centuries, so what if the spread of Graeco/Roman culture reachd Africa?

How would this affect the predominantly pastoralist peoples of Ethiopia?
How would this affect the rise of large, stable states in Sub-Saharan Africa?
Assuming Christianity arises in the Roman Empire in this reality, how would this affect the spread of Christianity in Africa and even India?

[Cynovolans]

I would assume Nubia would remain part of the Greek Orthodox Church (Or make a branch of their own Orthodox Church). Because from what I understand after the Arabs took over Egypt, the Nubian kingdom(I think it was Makuria or Nobatia) started mingling with other branches of Christianity like Monophysitism and the Coptic church before Islam became the dominant religion.

A stronger Roman presence(Of course after Constantine's time) in Nubia could maintain the Orthodox Church being dominant among the region.