Hadrian was born in AD 76. His father died when he was ten and he was placed in the care of guardians, one of whom was to be the future emperor Trajan.
Hadrian soon embarked on a military career and served as a tribune in Germany. He accompanied the new Emperor Trajan to Rome and in 100 AD married Trajan's grand niece. Next he served in the first and second Dacian wars and was then appointed governor of Syria. These postings gave Hadrian a great deal of experience of both the Army and the Roman provinces.
In 117 AD Trajan died and it was announced that he had adopted Hadrian as his son and heir. At the time many people had grave doubts as to whether Trajan had actually adopted Hadrian. However when the army hailed him as Emperor; the senate had no option but to follow and endorse Hadrian as emperor.
Hadrian opinions on how the Empire was to be run were radically different from those of his predecessors. Trajan had believed that the empire was best served by wars of conquest. But while Hadrian shared Trajan's sense of duty, he believed that the empire had expanded enough and that the gains now needed to be consolidated.
To this end he immediately gave up some of Trajan's conquests in the east, although he held on to Dacia (possibly because of the large number of Roman settlers there and the valuable Gold mines). These were very controversial decisions at the time, with Hadrian's advisors trying to dissuade him. Hadrian didn't take these decisions because he wasn't interested in the provinces, far from it he was keenly interested in their welfare and spent a very large part of his reign on personal tours of inspection, but rather because he believed the empire had overexpanded.
Problems in Britain
Rather than fighting wars of conquest, Hadrian concentrated in fortifying the frontiers and dealing with any unrest within the empire.
At the start of Hadrian's reign, one of the trouble spots was Britain. There had been serious fighting, probably due to an invasion of the province from the north (possibly in cooperation with rebels inside the province). This may have been the cause of a remark in a letter from Frontos to the emperor Marcus Aurelius in AD 162.
'In Hadrians day, how many of our soldiers were killed by the Jews, how many by the Britons'
The first part is a reference to the Jewish revolt by Simeon Bar Kosiba, which saw the rebels take Jerusalem and took three years to crush. The second part could refer to the events at the start of his reign, although its also possible that it referred to attacks on the army during the building of Hadrian's Wall.
The war in Britain had been brought under control by the time of his visit in 122AD. However Hadrian had decided to resolve the problem once and for all and with this in mind Hadrian embarked for Britain accompanied by Aulus Platorius Nepos (who was to be the new governor of Britain) and the VI Victrix legion.