The objective of the first emperor Augstus was ultimate power for the Imperium Romanum. He wanted to achieve world conquest to introduce the Pax Romana to all the people.

But already at the end of his reign Augustus recognised that world conquest was impossible, even for the mighty Roman legions. The world was far bigger than previously thought and therefore Augustus advised his successor to keep the status quo of the empire.

With the idea of world conquest abandoned Rome needed frontier lines to protect and secure the empire against its enemies.

At first the Romans secured natural boundaries. The built forts, fortlets and most probably watchtowers along the rivers the defined the edges of the Roman Empire. Those river frontiers were called ripa and well-known examples are the frontiers along the Rhine and the Danube. But still Rome tried to control territories beyond those frontiers. Outpost in the barbaricum are very common and by the end of the first century AD the Romans not only focused on natural boundaries, they created now artificial frontiers lines. They were now able to incorporate i.e. fertile strips of land into the empire.

Usually the artificial frontiers consisted of several elements. Forts, fortlets and watchtowers had to supervise the chosen frontier line. Later a linear barrier had to prevent uncontrolled movement. The development of the Roman frontiers culminated in the second century AD. In AD 122 the emperor Hadrian ordered the building of a frontier line in Britain from sea to sea. Hadrian's Wall was built of stone from the Solway to the Tyne, about 3 m wide and more than 4 m high. It was the strongest frontier the Romans ever built.

Author: Erik Dobat