At the greatest extent of the Roman Empire, the southern border lay along the deserts of Arabia in the Middle East (see Romans in Arabia) and the Sahara in North Africa, which represented a natural barrier against expansion. The Empire controlled the Mediterranean shores and the mountain ranges further inland. The Romans attempted twice to occupy the Siwa Oasis and finally used Siwa as a place of banishment. However Romans controlled the Nile many miles into Africa up to the modern border between Egypt and Sudan.