Valerian and Gallienus were two of the most notable emperors during the Crisis of the Third Century. Valerian, and his son Gallienus, were declared co-emperors in 253 CE and worked tirelessly to reunite and rebuild the Roman Empire. Their work, however, was ultimately unsuccessful; Valerian was captured by Sassanid forces in the Middle East and Gallienus was assassinated by a rival claimant to the throne

During the Crisis of the Third Century, two breakaway empires were formed from territory controlled by the Roman Empire. These two empires were the Palmyrene Empire in the east and the Gallic Empire in the northwest. They both broke away from the Roman Empire during the reign of Gallienus. Gallienus ruled throughout much of the middle period of the Crisis of the Third Century and, in spite of his best efforts, was unable to prevent the splintering of the Roman Empire and incapable of leading the reunification movement.

In 235 CE the Roman army was, indeed, on the ropes from Germanic invasions in the North, but the most accurate answer here is the assassination of Severus Alexander by his own troops. The military problems in the North had persisted for sometime, but the real internal strife of the crisis began when the ruler of the Empire was murdered by his own troops as he tried to pacify the Germanic tribes.

The Palmyrene Empire was one of two breakaway empires of Rome which were formed during the Crisis of the Third Century (the other was the Gallic Empire). The Palmyrene Empire was situated in modern-day Syria, Egypt, and Asia Minor. It successfully defended Roman territory from the Sassanid Empire, but was eventually conquered by Aurelian and reabsorbed into the Roman Empire.

The Battle of Edessa, fought in 260 CE, was the first battle in which a Roman Emperor was captured by the forces of the enemy. The emperor in question was Emperor Valerian, who ruled during the turbulent period known as the Crisis of the Third Century. After Valerian’s capture, his son Gallienus ruled as the sole Emperor.

The Battle of Margus was fought in 284 CE, between the forces of Diocletian and the forces of the Emperor Carinus. The battle ended in victory for Diocletian and allowed him to take control of the entire Roman Empire. The Battle of Margus is one of the last battles of the Crisis of the Third Century, as shortly thereafter Diocletian was able to enact a series of reforms which temporarily strengthened the Roman Empire.

The Battle of Chalons was fought in 274 CE, during the later years of the Crisis of the Third Century. The battle ended in victory for the forces of the Roman Empire, led by Aurelian, and defeat for the forces of the Gallic Empire, led by Tetricus. The battle resulted in the end of the Gallic Empire and its absorption back into the Roman Empire.

The Battle of Edessa was fought in the third century between the armies of the Roman Empire, led by Emperor Valerian, and the armies of the Sassanid Empire. It ended in absolute victory for the Sassanid forces and the capture of the Roman Emperor.

In the third century CE, the Roman Empire underwent a period of fifty years in which power was heavily decentralized. During this period, there were countless claimants to the position of emperor and no political uniformity in the Roman Empire. For a brief period, the Roman Empire was divided into three territories, each ruled by a different emperor. Eventually, the Roman Empire was stabilized under the rule of Aurelian. The Crisis of the Third Century came to an end shortly thereafter with a series of reforms made by the Emperor Diocletian.

The Battle of Emesa was fought in 272 CE between the forces of the Roman Empire, led by Aurelian, and the forces of the breakaway Palmyrene Empire. It ended in defeat for the Palmyrene Empire and allowed Aurelian to conquer and unify the Palmyrene Empire with the rest of the Roman Empire.