and the army. As the Senatorial class declined in political influence and more generals were recruited from the provinces this tension increased. Whenever the succession appeared uncertain, there was an incentive for any general with support of a sizable army to attempt to seize power, sparking civil war. The most recent example of this prior to the Crisis was the Year of the Five Emperors which resulted in the victory of Septimius Severus. After the overthrow of the Severan dynasty, for the rest of the 3rd century, Rome was ruled by a series of generals, coming into power through frequent civil wars which devastated the empire. Natural disasters The first and most immediately disastrous of the natural disasters that the Roman Empire faced during the Third Century was the plague. The Antonine Plague that preceded the Crisis of the Third Century sapped manpower from Roman armies and proved disastrous for the Roman economy. From AD 249 to AD 262, the Plague of Cyprian devastated the Roman Empire so much so that some cities, such as the city of Alexandria, experienced a 62% decline in population. These plagues greatly hindered the Roman Empire's ability to ward off barbarian invasions but also factored into problems such as famine, with many farms becoming abandoned and unproductive. A second and longer-term natural disaster that took place during the third century was the increased variability of weather. Drier summers meant less agricultural productivity and more extreme weather events led to agricultural instability. This could also have contributed to the increased barbarian pressure on Roman borders, as they too would have experienced the detrimental effects of climate change and sought to push inward to more productive regions of the Mediterranean. Foreign invasions Barbarian invasions came in the wake of civil war, plague, and famine. Distress caused in part by the changing climate led various barbarian tribes to push into Roman territory. Other tribes coalesced into more formidable entities (notably the Alamanni and Franks), or were pushed out of their former territories by more dangerous peoples such as the Sarmatians (the Huns did not appear west of the Volga for another century). Eventually, the frontiers were stabilized by the Illyrian Emperors. However, barbarian migrations into the empire continued in greater and greater numbers. Though these migrants were initially closely monitored and assimilated, later tribes eventually entered the Roman Empire en masse with their weapons, giving only token