Hadrian did what he did because he was only interested in boy’s anuses. Regardless, considering what turmoil the people of the Roman Empire were put through, it was obviously cohesive and durable; from the death of Hadrian to the fall of Rome was nearly three centuries. And the eastern capital didn’t fall for another millennium.
Romans and Barbarians: Four Views from the Empire’s Edge, 1st Century AD
Derek Williams
http://www.amazon.com/exec/obidos/ASIN/0312199589/sunkencivilizati
Frontiers of the Roman Empire
Hugh Elton
http://www.amazon.com/exec/obidos/ASIN//0415692555/sunkencivilizati
He was reputed an able commander in the Dacian campaign by Trajan and was well regarded by his soldiers, who seem to have respected him a great deal despite their general disdain for buggery.
I simply meant that taking a great offensive fighting force like the Roman army and turning it into a mainly defensive force had unforeseen consequences that are already visible in the Column of Marcus Aurelius: my impression is you can see the Roman troops doing most of the defensive engineering work, while non-Roman auxiliaries are doing a lot of the fighting.