Dealing with the external threat required a different approach. The Rhine River was not an impermeable barrier and Germanic brigands (latrones) were free to cross at will. Neither was there a Roman standing army on the Left Bank to intercept them when they raided. Just as he done had twenty years before, Agrippa travelled to the Rhine to critically assess the situation for himself. He found the Ubii once again under direct attack at their rear from the Suebi, a broad coalition of war bands which was moving ever southwestwards and encroaching aggressively on the territory of their neighbours.¹²² It seems the Ubii sent a deputation calling on their Roman allies to provide them sanctuary. In response, Agrippa made an extraordinary decision. ‘By their own consent,’ writes Strabo, ‘they were transferred by Agrippa to the country this side of the Rhenus’.¹²³ They founded a settlement called Oppidum Ubiorum, the precursor to modern Cologne. The agreement came with conditions, however. Tacitus mentions that the Ubii were relocated specifically so that they could assist the Romans in guarding that section of the river.¹²⁴ The archaeological evidence suggests that a Roman army was based here at different times over several years, but that the successive military encampments were probably sited some distance away from the civilian settlement.¹²⁵

It may also have been at this time that work began on an urban settlement (civitas) for the Treveri nation whose territory extended between the Rhine and Maas rivers. During Iulius Caesar’s Gallic War T. Labienus had defeated and killed their leader Indutiomarus and broken the Treveran resistance.¹²⁶ Expelled from their strongholds, such as the hill fort at Hunnering – or ‘Circle of the Huns’ – located at Otzenhausen, St. Wendel, in the Rhineland-Palatinate, this crushed nation had been largely left to its own devices.¹²⁷ A new town was established – probably initially called Oppidum Treverorum – on the banks of the Mosella (Moselle) River where modern Trier now stands. In combination with the Ubii some 190km (118 miles) to the north, Agrippa had established a nominal buffer zone between the people across the Rhine and the Galli to the south, where local allies – rather than Roman troops – provided the means to defend their home turf from incursions by invaders from the north.¹²⁸ His act of diplomatic generosity was a win-win for all parties.

Remarkably, despite Iulius Caesar having invested almost a decade to conquer the sixty Gallic tribes, little had been done to develop the population and its resources through urban or economic development. Its nations were still divided among the three parts Caesar described in his Commentaries on the Gallic War – Aquitania, Celtica and Belgica – as they had before the protracted conflict. Resentments among the surviving tribal members festered and it may have been these infractions which required Agrippa’s intervention. It would have been evident to Agrippa as he traversed the country that the old ways of the Iron Age population had been largely unaffected by annexation into the Roman Empire. Pacification could not be achieved by brute force alone. The tribal leadership needed a stake in the new economy; the mass of the population had to have a greater role in the society for Rome to win their loyalty.

The centre of Roman control for the region was a colonia Iulius Caesar’s deputy L. Munatius Plancus had founded for his retiring legionaries in 43 BCE when he was appointed Gaul’s first governor.¹²⁹ It stood in the heartland of the Aedui nation, which had for most of its history, barring a short episode as allies of Vercingetorix, been pro-Roman.¹³⁰ Built on the granite acropolis of Fourvière, formed by the erosion over millennia of the confluence of the rivers Rhône (Rhodanus) and Saône (Arar), it initially took the name of Colonia Copia Felix Munatia – in a flamboyant salute to the founder’s own family’s good luck but later known as Lugdunum (modern Lyon) – and was laid out in the grid-iron street plan so beloved of Roman surveyors (map 14). Probably anticipating he would be staying for some time in the region, Agrippa commissioned a new home for himself and his entourage. Positioned on the highest point of the city, it was a palatial building, measuring 37m (121.4ft) by 61m (200.1ft) with a symmetrically axial ground plan reminiscent of a military praetorium.¹³¹ Revealing its owner’s taste, it included two internal partially covered atria with peristyles in the Italian style and featured mosaic floors, painted walls and baths. From its main room Agrippa had a spectacular east-facing view across the valley of the Saône – reminiscent of the Villa Boscotrecase in Campania and its view of the Bay of Naples – where he could watch the sun rise in the morning.

The city was well positioned with access by the Rhône River to the Mediterranean coast to the south. There the great urban centres of Arausio, Arelate and Colonia Nemausus (Nîmes) in urbane Gallia Narbonensis (or Provincia ‘the province’, as some still referred to it) demonstrated what could be done with encouragement from Roman investors. The region to the north and west was, to all intents and purposes, virgin territory for exploitation through industry and trade. Moving people and goods across all compass points of the three Gallic provinces was hampered by the lack of a road network and, recognizing the fact, Agrippa was the most likely catalyst of much-needed change.¹³² The same highways would enable Roman troops and their supplies to move swiftly to quell future rebellions. Soon after his arrival, work began on three great roads radiating out from Colonia Copia westward to the Atlantic coast, terminating at a Mediolanum Santonum (modern Saintes), south via Vienna (Vienne) to the Mediterranean, east to Alpes Graiae at Axima (Aime) and north to his newly founded Oppidum Ubiorum on the Rhine.¹³³