How was the Roman Empire before 476?
GEOGRAPHICALLY, the borders of the Roman Empire, which fluctuated throughout the empire's history, were a combination of natural frontiers (most notably the Rhine and Danube rivers) and man-made fortifications (ie limes) which separated the lands of the empire from the barbarian countries beyond.
Limes (fortified walls) are man-made border fortifications of the Roman Empire.
In Brittania, the Empire built two walls [(Limes Britannicus: 1. Antonine wall (North) and 2. Hadrian wall (South)] one behind the other.
In Mauretania, there was a single wall (Limes Tripolitanus) with forts on both sides of it.
In other places, such as Syria and Arabia (Limes Arabicus), there wasn't a continuous wall; instead there was a net of border settlements and forts occupied by the Roman army.
In Germania Magna (modern Germany), Dacia (modern Romania), Limes Germanicus and the Limes Moesia (the conjunction of two, and sometimes three, lines of vallum, with a Great Camp and many minor camps spread through the fortifications).
Borders of the Roman Empire
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 was completely on the far side of the Danube so the Limes Moesia was built; and the province of Germania Magna was the land between the Rhine, the Danube and the Elbe so the Limes Germanicus was built.
In Great Britain, Hadrian built the Hadrian wall in 122 and Antonius Pius built the Antonine Wall between 142 and 144 to protect the province of Britannia from the Caledonians.
The eastern borders changed many times, of which the longest lasting was the Euphrates river. The Limes Arabicus protected Syria and Arabia.
Limes Africanus built by Septimius Severus was expanded by expanded and becomes the Limes Tripolitanus in the second century.
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 North Atlantic Ocean served as the natural barrier.
POLITICALLY, the emperor Diocletian (284-305) saw the vast empire as ungovernable, and therefore split the empire in half and created two equal emperors to rule under the title of Augustus. In doing so, he effectively created what would become the Western Roman Empire and the Eastern Roman Empire. In 293, the authority was further divided, as each Augustus took a junior Emperor called a Caesar to provide a line of succession. This constituted what is now known as the Tetrarchy ("rule of four"). The transitions of this period mark the beginnings of Late Antiquity. War erupted among the leaders which resulted to civil wars. In other words, there was political instability within the empire itself.