When the much-hated Emperor Domitian was assassinated, the conspirators asked Nerva to replace him. Nerva had come from a senatorial family from Narnia, in Umbria, and had held the position of consul, so the 66-year old was suitable. He swore and kept an oath not to execute senators, and made restitution for some of his predecessor's abuses. Nerva is famous as the first of Gibbon's five good emperors and for handing over the reins of power to someone other than a biological relative. Nerva adopted the second of the good emperors, Trajan, in 97. Trajan was already Caesar at the time of Nerva's death, which may have happened on this day in A.D. 98, three weeks after the emperor suffered a stroke at the beginning of his fourth consulship.
"This day in ancient history" caveat: please see Unreliability of Dates.