Augustus

Virgil writes of a Caesar “whose empire / shall reach to the Ocean’s limits, whose fame shall end in the stars”; Horace begs the goddess of luck to “guard our young swarm of warriors on the wing now / to spread the fear of Rome / into Arabia and the Red Sea coasts.”

The phrase “Ocean’s limits” reminds us how small and fuzzy at the edges was the Roman world. Accurate navigational equipment not having been invented, most explorers—usually they were traders—did not travel very far from the Mediterranean.

The Romans believed that the world’s landmass was a roughly circular disk consisting only of Europe and Asia, and that it was surrounded by a vast expanse of sea, Oceanus. They had no idea that the American and Australasian continents existed, nor that there was land beyond India. The landmass itself surrounded the Mediterranean Sea and Greece and Italy. The island of Britannia perched on its northwestern edge. The Roman empire took up a large part of the world as its inhabitants believed that world to be, and it was very tempting for its ambitious rulers to dream that they might one day conquer it all.

Maps were rare in the classical time; the first known world maps appeared in fifth-century Athens. Borrowing from Alexandrian models, the Romans, with their imperial responsibilities, recognized the practical importance of cartography. A world map was commissioned by Julius Caesar, probably as part of a triumphal monument he built on the Capitoline Hill, which showed him in a chariot with the world, in the form of a globe, at his feet.

Augustus commissioned his deputy, Agrippa, to work on a more detailed map, the orbis terrarum or “globe of the earth.” This showed hundreds of cities linked by Rome’s network of roads; it was based on reports sent in by Roman generals and governors, and by travelers. The result was a broadly recognizable picture, although distances and shapes became less and less accurate the farther places were from Rome.

The main purpose of the map was as an aid for imperial administrators, provincial governors, and military commanders; as a visual representation of the empire, it was also a powerful metaphor of Roman power. The map was painted or engraved on the wall of the Porticus Vipsania, a colonnade built by Agrippa’s sister, and was on permanent public display. Copies on papyrus or parchment were made for travelers, or information copied down.

As we have seen, Augustus and Agrippa spent many years abroad in different corners of the empire. Between 27 and 24 B.C., the princeps was in Gaul and Spain; between 22 and 19 B.C. in Greece and Asia; and between 16 and 13 B.C. in Gaul. Meanwhile, Agrippa spent 23 to 21 B.C. in the east, 20 and 19 in Gaul and Spain, and 16 to 13 B.C. in the east again. They spent their time quelling revolts, reforming or reviewing local administrations, and, above all, superintending the consolidation and expansion of the empire.

It is hard to tell whether the two men reacted to circumstances as they arose or pursued a long-term strategy. The impression is given of an orderly progression in the years that followed Actium from one priority to another. As we have seen, the eastern provinces and client kingdoms were reorganized. The frontier of Egypt was pushed southward and contact was made with the Ethiopians. An attempt was made to conquer the Arabian Peninsula, which failed. The negotiations with the Parthians were brought to a successful conclusion. Gaul and Spain were pacified.

A glance at the orbis terrarum showed that three great interrelated challenges were yet to be answered. First, the Alps were in the hands of fierce tribes and it was impossible to reach the eastern provinces by land around the top of the Italian peninsula. Second, the frontier of Macedonia was vaguely defined and hard to defend. Third, although the river Rhine, the existing Gallic frontier, ran from the North Sea to the Alps, there was constant westward pressure on it from Germanic tribes.

The ideal solution would be, first, to win control of the Alps and then move north to establish a defensible frontier lined with legions along the river Danube. In this way, buffer provinces in the north would protect Italy and Macedonia from direct attack. If the Rhine and the Danube were to mark the empire’s permanent boundary, a major strategic weakness would be likely to cause trouble in the future. This was that the heads of the two rivers formed a salient with its apex where the modern city of Basel stands today. The salient would allow hostile German tribes to operate on interior lines, giving them a huge military advantage.

So the final step would be to invade Germany and create a new frontier at the river Elbe. This would eliminate the salient and create a border roughly in a straight line between the North Sea and the Black Sea. Also, the territory thus gained would helpfully protect Gaul from eastern marauders.