Marcus Cocceius Nerva (November 8, 30 CE–January 27, 98 CE) ruled Rome as emperor from 96–98 CE following the assassination of  Emperor Domitian. Nerva was the first of the "five good emperors" and was the first to adopt an heir who wasn't part of his biological family. Nerva had been a friend of the Flavians without children of his own. He built aqueducts, worked on the transport system, and built granaries to improve the food supply.

A member of a distinguished senatorial family, Nerva was distantly related by marriage to the Julio-Claudian house and had been twice consul (71 ce and 90) when, on the assassination of the emperor Domitian, he became emperor.

Some historians speculate that Nerva may have been involved in the conspiracy to kill Domitian. At the very least, it seems likely that he was aware of it. On the same day, the Senate proclaimed Nerva emperor. When appointed, Nerva was already well into his sixties and had health issues, so it was unlikely he would rule for long. In addition, he had no children, which raised questions about his successor; it may be that he was selected specifically because he would be able to handpick the next Roman emperor. 
The initial months of Nerva's leadership focused on redressing Domitian's wrongs. Statues of the former emperor were destroyed, and Nerva granted amnesty to many whom Domitian had exiled. Following tradition, he executed no senators but did, according to Cassius Dio, “put to death all the slaves and freedmen who conspired against their masters.”

While many were satisfied with Nerva's approach, the military remained loyal to Domitian, in part because of his generous pay. Members of the Praetorian Guard rebelled against Nerva, imprisoning him in the palace and demanding the release of Petronius and Parthenius, two of Domitian's assassins. Nerva actually offered his own neck in exchange for those of the prisoners, but the military refused. Finally, the assassins were captured and executed, while Nerva was released.

There is no record that Nerva married, and he had no biological children. His solution was to adopt a son, and he selected Marcus Ulpius Traianus, Trajan, the governor of Upper Germany. The adoption, which took place in October of 97, allowed Nerva to placate the army by selecting a military commander as his heir; at the same time, it allowed him to consolidate his leadership and take control of the provinces in the north. Trajan was the first of many adopted heirs, many of whom served Rome extremely well. In fact, Trajan's own leadership is sometimes described as a "golden age."  
While Nerva retained power, his confidence was shaken. He spent much of the remainder of his 16-month reign attempting to stabilize the empire and ensure his own succession. Among his achievements were the dedication of a new forum, repairing roads, aqueducts, and the Colosseum, allotting land to the poor, reducing taxes imposed on Jews, instituting new laws limiting public games, and exercising greater oversight over the budget.