<P> In continental Europe, the borders were generally well defined, usually following the courses of major rivers such as the Rhine and the Danube . Nevertheless, those were not always the final border lines; the province of Dacia, modern Romania, was completely on the far side of the Danube, and the province of Germania Magna, which must not be confused with Germania Inferior and Germania Superior, was the land between the Rhine, the Danube and the Elbe (Although this province was lost three years after its creation as a result of the Battle of Teutoburg Forest). </P> <P> In Great Britain both Hadrian and Antoninus Pius built defences to protect the province of Britannia from the Caledonians . Hadrian's Wall, constructed in 122 held a garrison of 10,000 soldiers, while the Antonine Wall, constructed between 142 and 144, was abandoned by 164 and briefly reoccupied in 208, under the reign of Septimius Severus . </P> <P> The eastern borders changed many times, of which the longest lasting was the Euphrates river, eventually to be left behind as the Romans defeated their rivals, the Parthians, with the march on their capital, Susa in 115 . The Parthians were a group of Iranian peoples that ruled most of Greater Iran that is in modern - day Iran, western Iraq, Armenia and the Caucasus . In 118 Hadrian decided that it was in Rome's interest to re-establish the Euphrates as the limit of its direct control . Hadrian returned to the status quo ante, and surrendered the territories of Armenia, Mesopotamia, and Adiabene to their previous rulers and client - kings and didn't attempt to romanize the Parthian Empire . </P> <P> At the greatest extent of the Empire, the southern border lay along the deserts of Arabia in the Middle East 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 . </P>

Compare the boundaries of the roman empire with those of the byzantine empire