Question

what natural barrier formed the southern border of the roman empire? the mediterranean sea the alps mountain range the black sea the sahara desert

Explanation:

The Sahara Desert was a significant natural barrier to the south of the Roman Empire, limiting expansion and providing a degree of protection. The Mediterranean Sea was to the south of some parts but not the primary southern - border barrier. The Alps were to the north and the Black Sea to the east.

Answer:

The Sahara Desert