The key element of Trajan's administrative reign was the return of favorable relations with the aristocracy. Much like Augustus, Trajan readily delegated governing authority, and unlike previous 'emperors' there was a fundamental shift from the use of the freedman as political advisor and confidant back to the traditional Senate and Equestrian classes. During his near 20 year reign, he held the consulship only 6 times (contrasted by the 34 consulships held by the Flavians in the quarter century that they held power) while returning it to a position of honor in which numerous friends and allies openly served multiple terms.
At the same time such delegation of power was made with the intent of centralizing Roman government rather than allowing the corruption of past semi-independent provincial authority. The position of the curatores (a financial officer of the imperial government) was expanded upon to limit corruption and solidify standard practices of provincial rule. In these representatives Trajan placed the utmost trust as illustrated by the letters of Pliny the younger, who served Trajan in such a capacity in Bithynia et Pontus. In fact, Trajan expected these officers to function in much the same capacity as military subordinates, using their own discretion for most decisions and deferring to emperor only in matters of extreme importance.
Despite his attention to provincial government and the expansion of grand public welfare measures such as the alimenta, Trajan was not a reformer. The alimentary system of providing food and general welfare to the citizenry may have been advanced far beyond any previous gestures (so much so that the general complacency of Romans was referred to as 'panem et circenses' or bread and circuses by the contemporary Satirist Juneval), but its expansion was not a concept conceived by Trajan, nor was it simply intended as aid for the poor. Trajan understood the importance of Latin and Italian origins to the overall health of the empire and the alimenta largely encouraged the birth rate in Rome and Italy. As a life long man of the military, he also observed what was certainly deemed a dangerous trend towards barbarization of the legions, which could be slowed or reversed through these social programs. His view of Christianity, preserved by Pliny in his numerous letters, shows a general indifference provided they recognize the authority of the Roman gods, despite later accusations of intolerance by the Christian author Tertullian.
In addition to the alimenta, Trajan sponsored imperial building projects that touched all corners of the empire. From his military monument and bridge building efforts in Dacia to the famed Trajan's column in Rome, he relied upon his famed architect Apollodorus of Damascus for a wide array of improvements. Included in the more grand of these projects was Trajan's Forum, the largest of any such fora in the city, the Markets of Trajan which were built as the Roman equivalent of a modern shopping mall and the imperial baths which used the foundations of Nero's Domus Aurea (Golden House) and were fed by a newly constructed aqueduct (the Via Traiana). Shipping throughout the empire was increased through port expansion including that of Ostia (Rome's harbor on the Tiber and the Mediterranean). Road construction was expanded throughout the empire, the most well known being the Via Traiana, which provided a better alternative from Rome to Brundisium than the famous Via Appia (Appian Way). Along this route, one of southern Italy's most preserved Roman monuments was built; the Arch of Beneventum which was constructed to highlight Trajan's many great achievements.
Trajan's reign too was notable for inclusion of women in imperial public life. Having no children of his own and a considerably small primary family, the influence of his wife and sister is perhaps unrivalled in Roman history. Unlike such previous imperial women as Livia (wife of Augustus), Messalina and Agrippina (wives of Claudius with the latter being the mother of Nero), the women in Trajan's life were considered positive influences and were honored for their service to the empire rather than vilified in the historical record. Pompeia Plotina, Trajan's wife and Marciana, his sister were both honored with the title of Augusta in AD 105. Marciana's daughter Matidia went on to be honored in the same way upon her mother's death and she and Pompeia were instrumental in the accession of Hadrian after Trajan's passing. To illustrate the importance in public sentiment Hadrian, in order to cement his connection to Trajan, was married to Sabina (the daughter of Matidia) and remained so despite years of mutual loathing and his own suspected homosexual preferences.
The emperor however, despite his many achievements in Rome as a civilian ruler was a still a general at heart. Expansion in the east, including previously uncontrolled portions of Syria and Arabia Petraea (annexed in AD 105), put Rome into a position which controlled critical strategic trade junctures between east and west. As such, affairs in Armenia, long contested for political influence between Rome and the Parthian Empire came to a head by AD 113. Parthia had placed a candidate upon the throne of Armenia that did not meet with Roman approval and Trajan sought to put an end to Parthian rivalry once and for all.