Europe 263: Limesfall
With Odaenathus securing the East, Gallienus turned to Postumus and his ‘Gallic Empire’ in the West in 262/263. In the ensuing struggle, Gallienus regained control of Raetia but was unable to break through into Gaul. This stalemate left the Agri Decumates exposed, persuading both Roman factions to abandon the old frontier by pulling their garrisons back to the upper Rhine and Danube.
The rival Roman regime led by Postumus and his successors in Gaul (260–274) is often referred to as the Gallic Empire by modern historians. This term has no real historical basis; identity-wise, the Gallic emperors were simply Roman usurpers who successfully held out in Gaul for 14 years, but lacked the strength to take Rome.
262? Gallienus in Raetia▲
In 262 the Roman emperor Gallienus fought the usurper Postumus in a number of battles and eventually defeated him, although not decisively. It was probably at this point that Gallienus regained control of Raetia and, as a result, placed a damnatio memoriae on Postumus in the province and struck his name from inscriptions such as the Augsburg Victory Altar. Little else is known of this conflict between these two rivals, but it would be followed by an uneasy truce which lasted until 265.
262–263 Odaenathus’ First Persian Campaign▲
In spring 262, with the backing of Gallienus, Odaenathus of Palmyra attacked the Persian garrisons still in occupation of Edessa, Carrhae, and Nisibis and drove them from the Roman Empire. The Palmyrene–Roman forces then crossed into Persia, sacked Nehardea, and, in late 262/early 263 besieged the Persian capital Ctesiphon. However, Odaenathus was unable to capture the city in the face of Persian reinforcements and eventually withdrew with many prisoners and much booty. The Roman border fortress of Dura-Europus, destroyed by the Persians the previous decade, was left abandoned.
Shortly after Aurelius Theodotus arrived in Egypt and brought an end to Mussius Aemilianus’ usurpation, a second rebellion broke out under Memor. Memor was of Moorish origin and in charge of the vital Egyptian corn supply, but was swiftly killed by Theodotus, even before he could be proclaimed Emperor. With Egypt now pacified, Gallienus made Theodotus prefect.
The stalemate that developed between Gallienus and Postumus in 262/3 over Raetia and Upper Germania exposed the fortifications of the Agri Decumates to both Roman and barbarian threats. In response, Gallienus’ garrisons appear to have pulled back to the Danube and Postumus’ to the Rhine, essentially abandoning the region. Nonetheless, although the Alemanni cautiously moved in over the following years, a small Roman population would persist in the Agri Decumates for many decades afterwards.