Question: What philanthropic Roman emperor ruled during the time of the group of ten cities on the eastern frontier of the Roman Empire that were centers of Greek and Roman culture in an otherwise Semitic-speaking region?

Context articles: Decapolis
List of monarchs of Prussia
Byzantine Empire
History of the Byzantine Empire
Fall of the Western Roman Empire
Decapolis (disambiguation)
Trajan
Western Roman Empire
Executive magistrates of the Roman Empire
Senate of the Roman Empire

The Decapolis (Greek: Δεκάπολις "Dekápolis", Ten Cities) was a group of ten cities on the eastern frontier of the Roman Empire in the southeastern Levant.
 The cities were grouped together because of their language, culture, location, and political status, with each functioning as an autonomous city-state.
 Though sometimes described as a "league" of cities, it is now believed that they were never formally organized as a political unit.
 The Decapolis was a center of Greek and Roman culture in a region which was otherwise ancient Semitic-speaking peoples (Nabataeans, Arameans, and Judeans).
 In the time of the Emperor Trajan, the cities were placed into the provinces of Syria and Arabia Petraea; after a later reorganization several cities were placed in Syria Palaestina and later Palaestina Secunda.
 Most of the Decapolis region is located in modern-day Jordan, but Damascus is in Syria and Hippos and Scythopolis are in Israel.
The monarchs of Prussia were members of the House of Hohenzollern who were the hereditary rulers of the former German state of Prussia from its founding in 1525 as the Duchy of Prussia.
 The Duchy had evolved out of the Teutonic Order, a Roman Catholic crusader state and theocracy located along the eastern coast of the Baltic Sea.
 The Teutonic Knights were under the leadership of a Grand Master, the last of whom, Albert, converted to Protestantism and secularized the lands, which then became the Duchy of Prussia.
 The Duchy was initially a vassal of the Kingdom of Poland, as a result of the terms of the Prussian Homage whereby Albert was granted the Duchy as part of the terms of peace following the Prussian War.
 When the main line of Prussian Hohenzollerns died out in 1618, the Duchy passed to a different branch of the family, who also reigned as Electors of Brandenburg in the Holy Roman Empire.
 While still nominally two different territories, Prussia under the suzerainty of Poland and Brandenburg under the suzerainty of the Holy Roman Empire, the two states are known together historiographically as Brandenburg-Prussia.
 Following the Second Northern War, a series of treaties freed the Duchy of Prussia from any vassalage to any other state, making it a fully sovereign Duchy in its own right.
 This complex situation (where the Hohenzollern ruler of the independent Duchy of Prussia was also a subject of the Holy Roman Emperor as Elector of Brandenburg) laid the eventual groundwork for the establishment of the Kingdom of Prussia in 1701.
 For diplomatic reasons, the rulers of the state were known as the King in Prussia from 1701 to 1772; largely because they still owed fealty to the Emperor as Electors of Brandenburg, the "King in Prussia" title (as opposed to "King of Prussia") avoided offending the Emperor.
 As the Prussian state grew through several wars and diplomatic moves throughout the 18th century, it became apparent that Prussia had become a Great Power that did not need to submit meekly to the Holy Roman Empire.
 By 1772, the pretense was dropped, and the style "King of Prussia" was adopted.
 Thus it remained until 1871, when in the aftermath of the Franco-Prussian War, the King of Prussia Wilhelm I was crowned German Emperor.
 From that point forward, though the Kingdom of Prussia retained its status as a constituent state of the German Empire, all remaining Kings of Prussia also served as German Emperor, and that title took precedence.
The Byzantine Empire, also referred to as the Eastern Roman Empire, was the continuation of the Roman Empire in the East during Late Antiquity and the Middle Ages, when its capital city was Constantinople (modern-day Istanbul, which had been founded as Byzantium).
 It survived the fragmentation and fall of the Western Roman Empire in the 5th century AD and continued to exist for an additional thousand years until it fell to the Ottoman Turks in 1453.
 During most of its existence, the empire was the most powerful economic, cultural, and military force in Europe.
 Both "Byzantine Empire" and "Eastern Roman Empire" are historiographical terms created after the end of the realm; its citizens continued to refer to their empire as the "Roman Empire" (Greek: Βασιλεία τῶν Ῥωμαίων , tr.
 "Basileia tôn Rhōmaiōn" ; Latin: "Imperium Romanum" ), or "Romania" (Ῥωμανία ), and to themselves as "Romans".
This history of the Byzantine Empire covers the history of the Eastern Roman Empire from late antiquity until the Fall of Constantinople in 1453 AD.
 Several events from the 4th to 6th centuries mark the transitional period during which the Roman Empire's east and west divided.
 In 285, the emperor Diocletian (r. 284–305) partitioned the Roman Empire's administration into eastern and western halves.
 Between 324 and 330, Constantine I (r. 306–337) transferred the main capital from Rome to Byzantium, later known as "Constantinople" ("City of Constantine") and "Nova Roma" ("New Rome").
 Under Theodosius I (r. 379–395), Christianity became the Empire's official state religion and others such as Roman polytheism were proscribed.
 And finally, under the reign of Heraclius (r. 610–641), the Empire's military and administration were restructured and adopted Greek for official use instead of Latin.
 Thus, although it continued the Roman state and maintained Roman state traditions, modern historians distinguish Byzantium from ancient Rome insofar as it was oriented towards Greek rather than Latin culture, and characterised by Orthodox Christianity rather than Roman polytheism.
The Fall of the Western Roman Empire (also called Fall of the Roman Empire or Fall of Rome) was the process of decline in the Western Roman Empire in which it failed to enforce its rule, and its vast territory was divided into several successor polities.
 The Roman Empire lost the strengths that had allowed it to exercise effective control; modern historians mention factors including the effectiveness and numbers of the army, the health and numbers of the Roman population, the strength of the economy, the competence of the Emperor, the religious changes of the period, and the efficiency of the civil administration.
 Increasing pressure from barbarians outside Roman culture also contributed greatly to the collapse.
 The reasons for the collapse are major subjects of the historiography of the ancient world and they inform much modern discourse on state failure.
Decapolis is group of ten cities on the eastern frontier of the Roman Empire in Syria and Judea.
Trajan ( ; Latin: "Imperator Caesar Nerva Traianus Divi Nervae filius Augustus" ; 18 September 538August 117 AD) was Roman emperor from 98 to 117AD.
 Officially declared by the Senate "optimus princeps" ("the best ruler"), Trajan is remembered as a successful soldier-emperor who presided over the greatest military expansion in Roman history, leading the empire to attain its maximum territorial extent by the time of his death.
 He is also known for his philanthropic rule, overseeing extensive public building programs and implementing social welfare policies, which earned him his enduring reputation as the second of the Five Good Emperors who presided over an era of peace and prosperity in the Mediterranean world.
In historiography, the Western Roman Empire consists of the western provinces of the Roman Empire at any one time during which they were administered by a separate independent Imperial court, coequal with (or only nominally subordinate to) that administering the eastern half.
 Both "Western Roman Empire" and "Eastern Roman Empire" (or "Byzantine Empire") are modern terms describing "de facto" independent entities; however, at no point did the Romans consider the Empire split into two, but rather considered it a single state governed by two separate Imperial courts out of administrative expediency.
 The view that the Empire was impossible to govern by one emperor was established by Diocletian following the disastrous civil wars and disintegration of the Crisis of the 3rd century, and was instituted in Roman law by his introduction of the Tetrarchy in AD 285, a form of government which was legally to endure in one form or another for centuries.
 The Western Court was periodically abolished and recreated for the next two centuries until final abolition by Zeno in 480, by which time there was little effective central control left in the area legally administered by the Western Court.
The executive magistrates of the Roman Empire were elected individuals of the ancient Roman Empire.
 During the transition from monarchy to republic, the constitutional balance of power shifted from the executive (the Roman King) to the Roman Senate.
 During the transition from republic to empire, the constitutional balance of power shifted back to the executive (the Roman Emperor).
 Theoretically, the senate elected each new emperor, although in practice, it was the army which made the choice.
 The powers of an emperor, (his "imperium") existed, in theory at least, by virtue of his legal standing.
 The two most significant components to an emperor's "imperium" were the "tribunician powers" ("potestas tribunicia") and the "proconsular powers" ("imperium proconsulare").
 In theory at least, the tribunician powers (which were similar to those of the Plebeian Tribunes under the old republic) gave the emperor authority over Rome's civil government, while the proconsular powers (similar to those of military governors, or Proconsuls, under the old republic) gave him authority over the Roman army.
 While these distinctions were clearly defined during the early empire, eventually they were lost, and the emperor's powers became less constitutional and more monarchical.
The Senate of the Roman Empire was a political institution in the ancient Roman Empire.
 After the fall of the Roman Republic, the constitutional balance of power shifted from the "Roman Senate" to the "Roman Emperor."
 Beginning with the first emperor, Augustus, the Emperor and the Senate were technically two co-equal branches of government.
 In practice, however the actual authority of the imperial Senate was negligible, as the Emperor held the true power of the state.
 As such, membership in the Senate became sought after by individuals seeking prestige and social standing, rather than actual authority.
 During the reigns of the first Emperors, legislative, judicial, and electoral powers were all transferred from the "Roman assemblies" to the Senate.
 However, since the control that the Emperor held over the senate was absolute, the Senate acted as a vehicle through which the Emperor exercised his autocratic powers.