when Valerian
entered Mesopotamia to relieve the blockade of Edessa, he was defeated by
the Persian king Sapor, and taken prisoner (258 A. D.). He died soon
afterwards in captivity. The Persians not only reoccupied Antioch but also
seized Tarsus in Cilicia and Caesarea in Cappadocia, and ravaged Asia
Minor to the shores of the Aegean Sea.

While Valerian was waging his ill-fated war in the East, the rest of the
empire was in a continual state of turmoil. In 257 the Goths and other
peoples overran Dacia, crossed the Danube and penetrated as far south as
Macedonia and Achaia. In 258 a revolt broke out in Mauretania. The Berber
tribesmen, led by an able chief, Faraxen, invaded the province of Numidia,
and were only reduced to submission by the capture of their leader (260
A. D.). At the same time the Alamanni broke into Raetia, and made their
way over the Alps into the Po valley. Gallienus hastened to the rescue and
defeated them near Milan. But in his absence in Italy the Franks crossed
the Rhine and poured in devastating hordes over Gaul and Spain. The Roman
possessions on the right bank of the Rhine were lost at this time and
never recovered.

*The empire of the Gauls.* At the news of the death of Valerian the
commander in Pannonia, Ingenuus, raised the standard of revolt. After
defeating him, Gallienus found another serious rival in Regalianus, whom,
however, he was likewise able to overcome. But at the same time (258
A. D.), Marcus Cassius Latinius Postumus, whom Gallienus had left in
command in Gaul, assumed the imperial title, after a victory gained over a
body of Franks. He was able to clear Gaul of its foes and make himself
master of Britain and Spain. Gallienus was powerless to depose him.
Postumus did not endeavor to establish a national Gallic state but
regarded himself as exercising the Roman _imperium_ in a portion of the
empire. He fixed his capital at Treves, and organized a senate and other
institutions on the Roman model. His coins bore the inscription _Roma
Aeterna_.

*Palmyra.* In the Orient the Persians were unable to retain their hold on
Syria and Asia Minor. Their withdrawal was in large measure caused by the
activities of Odaenathus, the ruler of the city of Palmyra, who inflicted
a severe defeat upon Sapor and recovered Roman Mesopotamia. Thereupon two
brothers, Fulvius Macrianus and Fulvius Quietus, sons of an officer who
had distinguished himself against the Persians, were acclaimed as emperors