Hadrian has been described as the most versatile of all Roman emperors, who "adroitly concealed a mind envious, melancholy, hedonistic, and excessive with respect to his own ostentation; he simulated restraint, affability, clemency, and conversely disguised the ardor for fame with which he burned." His successor Marcus Aurelius, in his "Meditations", lists those to whom he owes a debt of gratitude; Hadrian is conspicuously absent. Hadrian's tense, authoritarian relationship with his senate was acknowledged a generation after his death by Fronto, himself a senator, who wrote in one of his letters to Marcus Aurelius that "I praised the deified Hadrian, your grandfather, in the senate on a number of occasions with great enthusiasm, and I did this willingly, too [...] But, if it can be said – respectfully acknowledging your devotion towards your grandfather – I wanted to appease and assuage Hadrian as I would Mars Gradivus or Dis Pater, rather than to love him." Fronto adds, in another letter, that he kept some friendships, during Hadrian's reign, "under the risk of my life" ("cum periculo capitis"). Hadrian underscored the autocratic character of his reign by counting his "dies imperii" from the day of his acclamation by the armies, rather than the senate, and legislating by frequent use of imperial decrees to bypass the Senate's approval. The veiled antagonism between Hadrian and the Senate never grew to overt confrontation as had happened during the reigns of overtly "bad" emperors, because Hadrian knew how to remain aloof and avoid an open clash. That Hadrian spent half of his reign away from Rome in constant travel probably helped to mitigate the worst of this permanently strained relationship.