Trajan - Optimus Princeps

Did Trajan really deserve his reputation as the embodiment of all imperial virtues? Why did Dante, writing in the Middle Ages, place him in the sixth sphere of Heaven among the Just and Temperate rulers?
In this, the only biography of Trajan available in English, Julian Bennett rigorously tests the substance of this glorious reputation. Surprisingly, for a Roman emperor, Trajan comes through the test with his reputation relatively intact.