After Domitian's assassination in 96 following his reign of terror, Nerva proceeded to set a new tone. Elevated to emperor on September 18, 96, he released those imprisoned for treason, banned future prosecutions for treason, restored much confiscated property, and involved the Senate in his rule.
Nerva may have been approached by the conspirators against Domitian because he was elderly (61) and childless. He adopted Trajan, already a commander of the armies on the German frontier, in the face of rising difficulties in administering the empire.
Domitian (81 - 96)
Trajan (98 - 117)