Why did Nerva adopt Trajan as his successor in 97 CE?

In 97 CE, Nerva adopted Trajan as his successor primarily to secure the stability of the empire and ensure a peaceful transition of power. Nerva’s reign faced significant challenges, including reluctance from the military to accept his authority and his inability to protect those who had assassinated his predecessor, Domitian.12

By adopting Trajan—who was then serving as the governor of Upper Germany—Nerva chose a candidate who was highly respected by both the Senate and the army commanders. Trajan was an outstanding soldier, and his selection helped quell the unrest among the frontier legions, as he was viewed as a leader capable of commanding their loyalty. This decision allowed Nerva to bypass his own kinsmen in favor of a proven leader, effectively reconciling the interests of the military and the political elite to provide the empire with stable, careful government.32