FTP, name this emperor who succeeded Trajan in AD 117 and built a barrier in Britain.
His first major military experience came while serving on the Danube with the Second Legion Adjutrix.  Following his military service he developed a rivalry with his brother-in-law, Julius Servianus, that would last throughout his life.  The patronage of his predecessor's advisor, Lucius Sura; his predecessor's wife, Plotina; and a marriage to his predecessor's grand-niece, Vibia Sabina helped lead to this man being named heir.  He built a massive mausoleum, Castel Sant'Angelo, after the death of his lover, Antinous, and soon after named Antoninus Pius his successor.  FTP, name this emperor who succeeded Trajan in AD 117 and built a barrier in Britain.
His first major military experience came while serving on the Danube with the Second Legion Adjutrix.  
Publius Aelius Hadrianus