This is the best, most definitive, biography of the Emperor Hadrian, based on recent research. For example, studies of memorial stones for retired commanders who had served under Hadrian, as well as commemorative coins.
This book should remove any regard for Marguerite Yourcenar's "Memoirs of Hadrian" as history. Her book remains magnificent literature. She relied too much on Dio Cassius, who seems to have had some kind of animus toward Hadrian.
For example, Yourcenar repeats the assertion by Dio Cassius that Hadrian was born in Iberia, and spoke Latin poorly. In fact,points out Birley, at the time of Hadrian's birth, Hadrian's father was a senator, senators were required to reside in Rome if they were not assigned as governors outside of Rome, and Hadrian's father was not a governor then. Hadrian most probably was born either in Rome or at Tivoli, where the family had a country villa.