The soldier kings til Constantin
For the period of crises of the soldier kings is characterizing that that in this space of 50 years, between 235 and 285 reigned more than 20 emperors of which only one died a natural death. With the permanent multiple front-wars again outwardly enemies and the fights of the heir apparents one with another in the interior are mentioned the politic factors of the empire-crise of the 3rd century. It was added an economic going down of the worsest kind: decrease of commerce and business, misery of the proletariat, fall of the farmer in the serfdom to the landowner and a partial fall into the natural economic. First under caesar Diocletians (284 - 305) came with completely changed foundations a new stability.
Diocletian and Constantin (306 - 337) were the most important representatives of the Roman empire since the days of Augustus. Both were from Illyria (Jugoslavia). Under their regent the principate turned (in pursuance of Theodor Mommsen) into a imperial domination with an absolutistish tendency. Compulsive public measures affected the economic live, too: The free economic work of the civics got replaced from compulsy federations. National manufactory of arms, weaving mills, public mines and quarries arose. The extending of the military road net and the big plants of water supply (aqueducts) got pushed with the help of public labour conscription of work. But even this political measures couldn´t advert the crise for a long time. The fall of the municipal citizenship and the italian middle classes continued. The italian farmers weren´t less and less able to compete with the rich provinces. Only big latifund manufactures could survive this crise. They brought the rest of the small farmers in economy dependence. The try of many farmers to escape lot with migration from the country were prevented with the law of 332 what chained them to their clods. So came beneath the slavery the rustic serfdom.
Another strong problem of the empire was getting stronger German infiltration. Germans came as mercenaries, as slaves from the wars with the border tribes and as farmers into the rustic serfdom into the empire. Marc Aurel (160 - 180) promoted this development with the settlement of German colonies - rustic, on their clods chainded hereditary tenants - in depopulated regions. In the army the Germans could rise to the highest officers. Emperor Theodosius I took 382 the last step on this way: he took a whole West Gothic tribe into the Roman territory and bounded them for the defence of the empire. In the west of the empire this development led to the German seizure of power from the East German Odoaker and the dethronement of the last West Roman caesar Romulus Augustus. In the year 476 whereas the German were eliminated by the goverment in East Rome.
But lets get back to the great emperors Diocletian and Constantin. In the years 284 - 305 the emperor got to the dominus, the sovereign of all subjects. The by edicts realized administration, legislation and jurisdiction were suggested by Diocletian. The senate fell on the level of a rightless state-council. The self-administration of the towns and provinces was abolished, the military and the civic authority separated, a break with the old Roman traditions. A salaried officialdom came beneath the mercenarydom and the body of officers. Diocletian didn´t feel only as the dominus but also as Deus (god). The symbol of his divine government was the oriental diadem. The imperial cult became the imperial religion. But against him rose the resistance of the growing Christianity. That was why a big persecution of Christians started and it ended first with under Constantin who granted in the year 313 general liberty. Theodosius made the Christianity to the imperial religion.
And Diocletian was it who took the step what impressed the Occidental history decesive pu to the deep Middle Age: He divided the empire into a western and eastern half, but with the maintenance of the ideal unity of the empire. By this time were this two parts reigned by two emperors (Diocletian in the east and Maximian in the west). The capitals were Nicomedia in Asia and Milan. Constantin the Great (305 - 337) forced anew the unity of the empire but without compromising the net weigth of both parts. Byzantinum, what got the name Constantinopel, became the capital of the east (337). First since 395 was the real and definitive separation valid.
Constantin finished the idea of the theocraty in the dominat. The person of the emperor appeared as divine. The sovereign took his task to save the poor, women, infants and slaves seriously. This shows a number of edicts. He felt called upon to be the absolute sovereign and to rule the world in divine mission.
In the rule of lay came new drastic changes. The Ius gentium, the law of nations, came beneath the Ius civile from the law of the twelfe tables from the year 451 BC and completed the Ius praetorium, a kind of common law. This ius praetorium had always adjusted to the historical development. The emperor-time brought it in the lasting form (Edictum perpetuum of Hadrian). But the law of the nation blured the difference between citizen and non-citizen and became a strong connection link of the unity of the empire. The further development and interpretation of the right were executed in the emperor-time by the lawyers. But in the dominat were the edicts of the emperor the only sources of right. Justinian (527 - 565) finished this development with his gathering of earlier laws and important representations of lawyers, the Corpus iuris civilis. Everywhere where the Roman tradition of right took part or was felt afer-wards in the Occidental development was this gathering importan.
In the year 115 reached under Trajan the enormous extension of the empire her climax with the provinces Arabia, Armenia, Assyria, Mesopotamia and Dakia (today Romania). But even in the 3rd century some borders couldn´t get secured and kept unde the pressure of the Germans and of the New Persian empire under the Sassanids (226 -642). After the attack of the Huns from Interior Asia to South Russia (375) the borders set in strong motion. There subjected this Mongolish-Turkish tribe the East Gothes under their king Ermanarich while in the west Gothes found assimilation in the empire southern of the Danube, if they turned Christian.

The final decay of Rome

Used literature:
Dr. phil. Bleicken, Jochen et altera, 1963: Propyläen-Weltgeschichte - Rom. Die römische Welt. Propyläen Verlag, Berlin, Frankfurt, Wien.

Liberati, Anna Maria und Bourbon, Fabio 1996: Rom. Weltreich der Antike. Nebel Verlag, Erlangen. English original title: Ancient Rome.

Mommsen, Theodor 1953: Römische Geschichte. Buchclub EX LIBIRS, Zürich.