<P> The Empire suffered from multiple, serious crises during the third century, including the rise of the Sassanid Empire, which inflicted three crushing defeats on Roman field armies and remained a potent threat for centuries . Other disasters included repeated civil wars, barbarian invasions, and more mass mortality in the Plague of Cyprian (from 250 onwards). Rome abandoned the province of Dacia on the north of the Danube (271), and for a short period the Empire split into a Gallic Empire in the West (260--274), a Palmyrene Empire in the East (260--273), and a central Roman rump state . The Rhine / Danube frontier also came under more effective threat from larger barbarian groupings, which had developed better agriculture and larger populations . The Empire survived the Crisis of the Third Century, directing its economy successfully towards defence, but survival came at the price of a more centralized and bureaucratic state . Under Gallienus the senatorial aristocracy ceased joining the ranks of the senior military commanders, its typical members lacking interest in military service and showing incompetence at command . </P> <P> Aurelian reunited the empire in 274; and from 284 Diocletian and his successors reorganized it with more emphasis on the military . John the Lydian, writing over two centuries later, reported that Diocletian's army at one point totaled 389,704 men, plus 45,562 in the fleets, and numbers may have increased later . With the limited communications of the time, both the European and the Eastern frontiers needed the attention of their own supreme commanders . Diocletian tried to solve this problem by re-establishing an adoptive succession with a senior (Augustus) and junior (Caesar) emperor in each half of the Empire, but this system of tetrarchy broke down within one generation; the hereditary principle re-established itself with generally unfortunate results, and thereafter civil war became again the main method of establishing new imperial regimes . Although Constantine the Great (in office 306 to 337) again re-united the Empire, towards the end of the fourth century the need for division was generally accepted . From then on, the Empire existed in constant tension between the need for two emperors and their mutual mistrust . </P> <P> Until late in the fourth century the united Empire retained sufficient power to launch attacks against its enemies in Germania and in the Sassanid Empire . Receptio of barbarians became widely practiced: imperial authorities admitted potentially hostile groups into the Empire, split them up, and allotted to them lands, status, and duties within the imperial system . In this way many groups provided unfree workers (coloni) for Roman landowners, and recruits (laeti) for the Roman army . Sometimes their leaders became officers . Normally the Romans managed the process carefully, with sufficient military force on hand to ensure compliance, and cultural assimilation followed over the next generation or two . </P> <P> The new supreme rulers disposed of the legal fiction of the early Empire (seeing the emperor as but the first among equals); emperors from Aurelian (reigned 270--275) onwards openly styled themselves as dominus et deus, "lord and god", titles appropriate for a master - slave relationship . An elaborate court ceremonial developed, and obsequious flattery became the order of the day . Under Diocletian, the flow of direct requests to the emperor rapidly reduced and soon ceased altogether . No other form of direct access replaced them, and the emperor received only information filtered through his courtiers . </P>

What happened as a result of the fall of the roman empire