quality:correction, information:classification
Rise to power

Domitian's successor, Nerva, was unpopular with the army, and had been forced by his Praetorian Prefect Casperius Aelianus to execute Domitian's killers. Nerva needed the army's support to avoid being ousted. He accomplished this in the summer of 97 by naming Trajan as his adoptive son and successor, claiming that this was entirely due to Trajan's outstanding military merits. There are hints, however, in contemporary literary sources that Trajan's adoption was imposed on Nerva. Pliny implied as much when he wrote that, although an emperor could not be coerced into doing something, if this was the way in which Trajan was raised to power, then it was worth it. Alice König argues that the notion of a natural continuity between Nerva's and Trajan's reigns was an ex post facto fiction developed by authors writing under Trajan, including Tacitus and Pliny.

According to the Historia Augusta, the future Emperor Hadrian brought word to Trajan of his adoption. Trajan retained Hadrian on the Rhine frontier as a military tribune, and Hadrian thus became privy to the circle of friends and relations with whom Trajan surrounded himself. Among them was Lucius Licinius Sura, a Roman senator born in Spain and the governor of Germania Inferior, who was Trajan's personal friend and became an official adviser of the Emperor. Sura was highly influential, and was appointed consul for a third term in 107. Some senators may have resented Sura's activities as a kingmaker and éminence grise, among them the historian Tacitus, who acknowledged Sura's military and oratorical talents, but compared his rapacity and devious ways to those of Vespasian 's éminence grise Licinius Mucianus. Sura is said to have informed Hadrian in 108 that he had been chosen as Trajan's imperial heir.

As governor of Upper Germany (Germania Superior) during Nerva's reign, Trajan received the impressive title of Germanicus for his skilful management and rule of the volatile Imperial province. When Nerva died on 28 January 98, Trajan succeeded to the role of emperor without any outward adverse incident. The fact that he chose not to hasten towards Rome, but made a lengthy tour of inspection on the Rhine and Danube frontiers, may suggest that he was unsure of his position, both in Rome and with the armies at the front. Alternatively, Trajan's keen military mind understood the importance of strengthening the empire's frontiers. His vision for future conquests required the diligent improvement of surveillance networks, defences and transport along the Danube. Prior to his frontier tours, Trajan ordered his Prefect Aelianus to attend him in Germany, where he was apparently executed forthwith ("put out of the way"), and his now-vacant post taken by Attius Suburanus. Trajan's accession, therefore, could qualify more as a successful coup than an orderly succession.