Hadrianus 5, 1-2 and 11, 2

5 When he took over the government, Hadrian immediately reverted to an earlier policy, and devoted his energies to maintaining peace throughout the world. For at one and the same time those peoples Trajan had subjugated were in revolt, the Moors started making attacks, the Sarmatae were waging war, the Britons could not be kept under Roman control.

11 And so, having reformed the army in the manner of a king, Hadrian set out for Britain. There he corrected many faults and was the first to build a wall, 80 miles long, to separate the Romans and barbarians.