In late 275 the Roman Senate ended the post-Aurelian interregnum by appointing the aged Marcus Claudius Tacitus as emperor. Tacitus soon faced serious challenges: that winter Germanic tribes invaded Gaul while the Heruli overran much of Asia Minor. He defeated the Heruli in 276, but died—probably assassinated—while returning west, after a reign of just six months.
The Agri Decumates was lost to the Romans in c.262, regained by Aurelian and Probus in 275–8, and lost again sometime between 290 and 310. The losses here seem not so much due to any rise in power of the local Alemanni tribe, but Roman internal division. When rival Roman factions controlled Gaul and Raetia, as was the case in 262–274 and 306, the limes of the Agri Decumates were no longer defensible and had to be abandoned.
In late 275 the Roman Senate appointed the 75-year-old former consul Marcus Claudius Tacitus as emperor. Tacitus ruled for about six months, during which he restored some authority of the Senate and defeated the Heruli invasion of Asia Minor. He died at Tyana in June 276, most likely murdered by Syrian nobles who rejected the austerity measures imposed by their governor, his cousin.in wikipedia
In the winter of 275/6 Heruli from the Sea of Azov arrived in Pontus, claiming to have been recruited by the late Aurelian for his Persian war. When the Romans rejected their demands for payment, the Heruli sacked the province, raiding as far as Cilicia. Tacitus, who had traveled to Thrace to execute Aurelian’s assassins, crossed into Asia and defeated the invaders in a campaign that earned him the title Gothicus Maximus.in wikipedia
In late 275 the Franks, Alemanni, Longiones, and other tribes invaded Gaul, breaking through the fortified Limes Transrhenanus that connected the Rhine to the Danube. They quickly overran many small towns but were unable to breach the walls of the region’s cities. However, due to problems in the East, the Romans were unable to expel the barbarians until 277.in wikipedia