The Transition from Roman to Frankish Rule

A period of relative stability under emperors Valentinian I and Gratian (364-83) saw little change in the Rhineland conditions. The Roman government deepened its reliance on Frankish foederati in the late fourth and early fifth centuries against the Alemanni confederation as its own military power receded from the frontier provinces. No less than a Frankish king, Mallobaudes, served Gratian as his comes domesticorum by destroying King Macrianus of the Bucinobantes tribe in 374 (or 380) and then joining Gratian in defeating King Priarius of the Lentienses at the Battle of Argentovaria in 378. The Frankish mercenary Arbogast also rose through an effective military career to the title of magister militum of the entire western half of the Roman Empire and even began to rule de facto in the name of the young Valentinian II by 391. When in the following year he declared Valentinian dead by suicide and the rhetorician Eugenius as the next emperor, it was undeniable who the power behind the Western imperial throne was. Two years later Arbogast commanded yet another punitive campaign against his own Frankish people after the latter's recent severe plundering raids west of the Rhine, whereupon he even succeeded in recruiting fresh Frankish mercenaries to bolster his own standing in the ensuing peace treaty. A regular visitor there during this period, he restored Cologne's security and funded the refurbishing of a large public building (perhaps the praetorium or, alternatively, the thermal baths).

Like a latter-day Postumus, Arbogast's reign was short. He committed suicide only one year later, after losing the disastrous Battle of Frigidus against the Eastern emperor Theodosius I and his Visigothic mercenaries in September of 394. Yet while these political and military struggles for predominance over the Roman Empire transpired on the battlefield, the building boom still continued in Cologne despite the political unravelling of Roman authority in the West. Archaeological evidence makes clear that several buildings were going up at this time in the Rhine suburb along the shoreline, including a more than 100-meter-long public structure in today’s Hay Market (Heumarkt) and a mighty building of unknown purpose north of today's Old Market area (Alter Markt).