Ethiopia

I don't know about you, but when in the first film father Merrin mentioned how he met Pazuzu in East Africa a long time ago, I somehow always imagined the meeting taking place in Ethiopia.

Ethiopia has been a Christian country for 1700 years, it was the third state in the world to officially adopt Christianity as an official religion. Some of its churches are as old as Christianity in that region, and it is a land of great mystery and fascination, with its churches etched in stone, ancient monasteries and even the Arc o Covenant is believed to be kept in Ethiopia.

I think it would have been a much more logical place for the church that was Pazuzu's trap. Such architecture wouldn't be foreign to the region, because the Ethiopians kept close contact with the Byzantine Empire that clearly built the structure. Or it could have been a native Ethiopian building.

Placing a Byzantine/Roman church in a region that was very much outside the Roman world was highly illogical.