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?

<P0-S0> 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. <P0-S1>  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. <P0-S2>  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. <P0-S3>  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. <SEP> <P1-S0> Trajan ( ; Latin: "Imperator Caesar Nerva Traianus Divi Nervae filius Augustus" ; 18 September 538August 117 AD) was Roman emperor from 98 to 117AD. <P1-S1>  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. <P1-S2>  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. <SEP> <P2-S0> 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. <P2-S1>  The cities were grouped together because of their language, culture, location, and political status, with each functioning as an autonomous city-state. <P2-S2>  Though sometimes described as a "league" of cities, it is now believed that they were never formally organized as a political unit. <P2-S3>  The Decapolis was a center of Greek and Roman culture in a region which was otherwise ancient Semitic-speaking peoples (Nabataeans, Arameans, and Judeans). <P2-S4>  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. <P2-S5>  Most of the Decapolis region is located in modern-day Jordan, but Damascus is in Syria and Hippos and Scythopolis are in Israel. <SEP> <P3-S0> Decapolis is group of ten cities on the eastern frontier of the Roman Empire in Syria and Judea.