Crowned Emperor in 117AD, it would nearly be a full year before he took his seat in Rome.  With his life spent travelling in battle, he did not stay long.  In 121, he set out on a tour of his empire, inspecting the troops and examining frontier defences.  The Christian writer Tertullian called him rightly omnium curiositatum explorator - an explorer of everything interesting.

Travelling through Gaul and Germania, he came to Britain in 122.  And it is here that one of his most enduring monuments was built – “Hadrian’s Wall.”

The wall extended from coast to coast across the width of northern Britain; it ran for 73 miles from Wallsend (Segedunum) on the River Tyne in the east to Bowness on the Solway Firth in the west.  At every 1/3 Roman mile there was a tower, and at every mile a fort.The initial construction of the wall took approximately six years, and expansions were later made. Upon Hadrian’s death, his successor Antoninus Pius (138–161) decided to extend the Roman dominion northward by building a new wall in Scotland. The resulting Antonine Wall stretched for 37 miles (59 km) along the narrow isthmus between the estuaries of the Rivers Forth and Clyde. Within two decades, however, the Antonine Wall was abandoned in favour of Hadrian’s Wall, which continued in use nearly until the end of Roman rule in Britain (410).

Historia Augusta

p3 The Life of Hadrian
Part 1

And so, having reformed the army quite in the manner of a monarch, he set out for Britain,and there he corrected many abuses and was the first to construct a wall, eighty miles in length, which was to separate the barbarians from the Romans.

  He removed from office Septicius Clarus, the prefect of the guard, and Suetonius Tranquillus, the imperial secretary, and many others besides, because without his consent they had been conducting themselves toward his wife, Sabina, in a more informal fashion than the etiquette of the court demanded. And, as he was himself wont to say, he would have sent away his wife too, on the ground of ill-temper and irritability, had he been merely a private citizen. 4 Moreover, his vigilance was not confined to his own household but extended to those of his friends, and by means of his private agents he even pried into all their secrets, and so skilfully that they were never aware that the Emperor was acquainted with their private lives until he revealed it himself. 5 In this connection, the insertion of an incident will not be unwelcome, showing that he found out much about his friends. 6 The wife of a certain man wrote to her husband, complaining that he was so preoccupied by p37pleasures and baths that he would not return home to her, and Hadrian found this out through his private agents. And so, when the husband asked for a furlough, Hadrian reproached him with his fondness for his baths and his pleasures. Whereupon the man exclaimed: "What, did my wife write you just what she wrote to me?" 7 And, indeed, as for this habit of Hadrian's, men regard it as a most grievous fault, and add to their criticism the statements which are current regarding the passion for males and the adulteries with married women to which he is said to have been addicted, adding also the charge that he did not even keep faith with his friends.

 After arranging matters in Britain he crossed over to Gaul...