Map showing the biggest extension of Roman conquests in “Germania” during Augustus

In the north Roman occupation stopped at the Alps. In order to secure Cisalpine Gaul Augustus decided that it was necessary to conquer the whole Alpine range and by reducing the districts of Raetia and Noricum (roughly eastern Switzerland, the Tyrol and Austria) to advance the frontier to the Danube from Lake Constance to Vienna. He further judged that the southern Balkans would never be secure unless the Romans advanced northwards there also to the Danube. He thus planned a large-scale advance to the whole length of the Danube from Lake Constance to the Black Sea, with the establishment of new provinces in the conquered land of Raetia, Noricum, Pannonia and Moesia. The northern frontier of the Empire could thus be guarded by the Rhine and Danube. But communications would be shortened and the awkward re-entrant angle between the sources of the Rhine and Danube (in the Black Forest area) would be eliminated if the frontier was advanced eastwards over the Rhine to another river such as the Elbe and if this new frontier was joined to the Danube frontier near Vienna. This great plan would involve the conquest of western Germany and the reduction of the Marcomanni who lived in what is now Bohemia. We must now see in more detail how this vast scheme to advance to the Danube was successfully carried out and how various events induced Augustus to abandon his policy of advancing beyond the Rhine after it had been initiated with considerable success.

Communications over the Alps between North Italy and Transalpine Gaul required safeguarding, especially in the neighbourhood of the Great and Little St. Bernard Passes which were subject to raids by the tribe of the Salassi. Earlier indecisive campaigns (35-34 B.C.) were followed by more drastic action in 25 B.C. when Terentius Varro ruthlessly crushed the Salassi, while M. Vinicius was probably defeating the tribes further north in the Vallis Poenina (modern Valais). To guard the roads over the St. Bernard Passes a military colony was established at Augusta Praetoria (modern Aosta). Further south the Cottian Alps and the Pass of Mont Genevre were left in the hands of a native ruler M. Julius Cottius with the rank of a Roman prefect; a few Roman troops were posted at Segusio (modern Susa). Still further south the Ligurian tribes were checked by the establishment in 14 B.C. of a small province called Alpes Maritimae, governed by a military prefect. When P. Silius Nerva had cleared the valleys from Como to Lake Garda and the Upper Adige (17/16), Augustus entrusted the great advance to the Danube to his two stepsons. Tiberius, advancing from Gaul, defeated the Vindelici near Lake Constance, while his brother Drusus moved up from the south over the Resia and Brenner Passes to the valley of the Inn; together they swept forward to the Danube (15 B.C.). These victories were commemorated by Horace, who renewed his earlier songs of triumph, and by the erection of the Trophy of Augustus, naming forty-six subdued Alpine and Raetian tribes, which still survives at La Turbie, above Monaco.

The conquered area south of the Danube comprised two districts, Raetia and Noricum. The former was established as a new imperial province, administered at first by the governor of Gaul and subsequently by an equestrian prefect or procurator. At first two legions were kept near Augusta Vindelicorum (Augsburg), but after A.D. 9 it remained without legions until the reign of M. Aurelius; the commander of the armies of the Rhine was responsible for peace in Raetia and little attempt was made to Romanize the province. Noricum (roughly Austria) was incorporated in the Empire about 16 B.C., but it was not organized as a province until later (probably under Claudius); the governor of Pannonia to the east was responsible for its security.

Thus Rome had gained control of the territory up to the Danube from Vienna westwards. With the Alps and Spain now pacified, Augustus could turn to the crucial question of the northern frontier of the Balkans. In his earlier Illyrian campaigns (35-33) he had penetrated to Siscia on the Save in Pannonia and had defeated the Iapudes, Pannonii and Dalmatians. Thus in 27 it had been possible to make Illyricum a senatorial province; at the same time further south Achaea was detached from Macedonia, as a separate province, both being entrusted to senatorial administration. But the Pannonians were not really subdued. Fighting started again in 13, and this time Augustus determined that it should be decisive: first Agrippa (in 13) and then Tiberius conducted a series of campaigns (12-9) by which all Pannonia up to the Danube was brought under Roman rule: it was added to Illyricum, which since c. 12 had again become imperial. Further to the east other tribes were turbulent. In 29 Licinius Crassus, the governor of Macedonia, had ejected the Bastarnae from Thrace, reduced the Moesi and captured Serdica (modern Sofia). The Moesians were incorporated in Macedonia, but the Thracian tribes were left under their own rulers. Intermittent disturbances were followed by a general rising in Thrace which was crushed by L. Calpurnius Piso only after three years of hard fighting (c. 11-9); the loyal kingdom of the Odrysian Thracians was extended. Sometime later, probably in A.D. 6, Moesia was established as a province, though Thrace to its south remained under native rulers. Thus Roman control was established up to the Danube along its whole length from Switzerland to the Black Sea.

Before this frontier was finally settled it had to endure what may reasonably be called the Great Rebellion. In A.D. 6, while Tiberius was engaged on critical operations in Germany (see below), Dalmatia and Pannonia both rose in revolt, each led by a chief called Bato; Roman residents were massacred and if the enemy had united they might even have threatened the frontier of Italy itself. But Sirmium, a key position on the Save, was held by the legate of Moesia, and the Dalmatians wasted time attacking coastal cities; thus Tiberius was enabled to fight his way to Siscia which he held with five legions. The efficiency of the whole Augustan military system was now at stake, and the absence of a strong central reserve of troops nearly proved fatal: Augustus had reduced the forces of the Empire to a dangerously low level. When at last, however, some legions from the East reached Tiberius, he was able with an army of some 100,000 men to take the offensive and to crush the Pannonians in two campaigns (A.D. 7-8). The Pannonian Bato turned traitor, but was soon killed by his namesake who fought on. The following year (9) Tiberius planned a converging attack on Dalmatia, in which his nephew Germanicus won his spurs. The revolt was thus crushed. Pannonia was established as a separate imperial province, under a legatus Augusti pro praetore, and Illyricum was soon renamed Dalmatia. Tiberius had shown great military ability, but he could not rest on his laurels: news came of an overwhelming disaster to Roman forces in Germany.

Part of Emperor Hadrian’s Wall

Roman Auxillary

Britain was the sole island attacked by Rome outside the far less tidal waters of the Mediterranean, and Julius Caesar’s invasions in 55 and 54 B.C. therefore were bold steps. He claimed that they were necessary to end support for resistance to his conquest of Gaul (France). However, it was largely personal prestige and the dictates of politics in Rome that led to his expeditions, as they also did for the following expedition, that of the Emperor Claudius in A.D. 43. Caesar needed to show that the invasions were necessary for him to remain in control of the army, and he also wished to win glory.

In 55 B.C., Caesar did not move from his precarious bridgehead in Kent. The Romans were victorious in hard fighting, but the damage done to their ships by equinoctial gales and the scale of the resistance led Caesar to come to terms with the local tribes. The following year, however, in a reminder of the apparently inexorable persistence of a major state, Caesar led a larger invasion force. Landing in Kent, Caesar won a victory near Canterbury, defeating the tribal leader, Cassivellaunus, and crossed the Thames, seizing his capital, Wheathampstead. A settlement was then reached in which hostages and tribute were promised by the local rulers, before Caesar withdrew. The Romans had benefited from their opponents’ naval weakness, which meant that they could not contest the passage of the English Channel, and from their own fighting advantage once landed. The disciplined Roman infantry, with its body armor, javelins, and short swords, was more effective than that of the British, who had little body armor and lacked effective missile power. British chariots were vulnerable to Roman archers and their hill forts to siegecraft. Furthermore, as a demonstration of the problems posed by universal military service when in conflict with regulars, the British farmer-soldiers could not afford to be soldiers all the time, and their farming also made them vulnerable to Roman devastation.

Due to rebellion in Gaul, civil war, and the higher priority of the German frontier, Caesar’s expedition was not followed up until 43 A.D. when about 40,000 troops invaded. After an unopposed landing, probably in Kent, the Romans defeated a confederation of forces in three battles, two of which were caused by contested crossings of the rivers Medway and Thames. Claudius then arrived, with the first elephants seen in Britain, and received the surrender of Colchester. After he decided to make Britannia a Roman province, southern England was rapidly overrun. Prefiguring British imperialism in India, Malaya, and Africa in the nineteenth century, some rulers accepted client status, but there was also much fighting, with hill forts such as Maiden Castle outside modern Dorchester being stormed. This fortress, which belonged to the tribe of the Durotriges, survives as a striking manifestation of the task the Romans faced. The serried banks of the hill fort were calculated to break up an attacking charge. The innermost bank would have carried a palisade.

Caratacus, the leader of the Catuvellauni tribe, continued resistance from Wales, but was defeated in 50–51. In 60, a strong rebellion was launched when the Iceni tribe of East Anglia, enraged by vicious and corrupt Roman mismanagement and expropriation, and led by Queen Boudica, rebelled, storming the major Roman settlements: Colchester, London, and St. Albans, and slaughtering their inhabitants with great cruelty. However, as with the Indian Mutiny against English rule in 1857, there was no united response, in large part because there was no basis for political unity. For example, Cogidubnus, the client ruler of the Atrebates of Surrey, Sussex, and Hampshire, remained loyal to the Romans. The lack of a united response provided the key political context for decisive action by the regular forces, who moved rapidly, defeating Boudica’s army. She died, probably by suicide. The Iceni and their allies were then ‘‘pacified’’ with typical Roman brutality. The pace of Roman advance resumed in 71 with the subjugation of the Brigantes of northern England (71–73/74) and of Wales (73/74–76).

However, Highland Scotland was never conquered. Agricola, Roman Governor from 77 to 83, completed the conquest of Wales and northern England, and invaded Scotland, winning a notable victory at Mons Graupius, but only the Scottish lowlands were conquered. As a reminder of the difficulty of judging the environmental factor, in explaining developments it is possible to stress the difficulty of the highland terrain in the Roman failure, but also the quality of the defense. Although Agricola considered its conquest, Ireland was not attacked by the Romans, and, indeed, it was probably a task beyond Roman capacity.

Thereafter, the main theme in the military history of Britain under the Romans was defensive. The competing demands of the vulnerable Danube frontier meant a reduction in the considerable military effort devoted to Britain. By the early years of the second century, the Romans had abandoned their occupation of southern and central Scotland. Instead, they constructed Hadrian’s Wall, a 70-mile long fortified stone wall (with supporting forts such as Housesteads), built from about 122 by the Emperor Hadrian across Britain at its narrowest from Tyne to Solway.

Designed to mark a frontier, this was not the end of Roman attempts to move north, but none proved more than short-term, and the wall came to have a defensive function, stopping the Picts from raiding south. Hadrian’s successor, Antonious Pius, had ordered a fresh advance north. Eastern Scotland was occupied as far north as the river Tay, and a wall of turf on a stone base was built from the Firth of Forth to the Clyde in about 140. That line was held until about 163 or later, when Hadrian’s Wall again became the frontier. The Emperor Septimus Severus advanced into Scotland in 209–210, but, thereafter the frontier stabilized on the Tyne-Solway line.

Similarly, the ten forts of the Saxon Shore built from the 270s onward from Brancaster, Norfolk to Portchester, Hampshire, were intended to limit attacks on the east and south coasts of England by seaborne raiders from Germany. These forts, most of which had bastion towers, were designed to protect harbors and estuaries. The construction of town defenses from the third century also indicated an attitude of growing defensiveness in the face of outside attack. Challenges from outside included Picts from Scotland, Scots from Ireland, and Saxons from north Germany. Their attacks became serious in the 350s, while a successful invasion in 367 led to widespread devastation. Some additions to Britain’s defenses followed on the restoration of order.

Roman Britain was also weakened by the repeated inability of the Roman Empire to devise a consistently accepted system of imperial succession, and the willingness of military units to support their commanders in bids for power, although such bids were not continual. In the 400s, when Gaul was invaded by ‘‘barbarians,’’ a cutoff Britain backed its own emperor, Constantine III, who took a significant part of the military forces to Gaul. They did not return. The disillusioned Romano-Britons expelled his administrators, and appealed to the true emperor, Honorius, for the restoration of legitimate rule, but he, hard-pressed in Italy, by Alaric, the Visigothic leader, who captured Rome in 410, could do no more than tell them to look to their own defense. This, the formal end of imperial government in 409, was the close of the Roman Empire in Britain.