Which succession system did the 'Five Good Emperors' primarily use?

The story behind the answer

Adoption is correct because the “Five Good Emperors”—Nerva, Trajan, Hadrian, Antoninus Pius, and Marcus Aurelius—mostly chose and legally adopted their successors based on merit, not bloodline. Nerva adopted Trajan; Trajan adopted Hadrian; Hadrian adopted Antoninus Pius on the condition he adopt Marcus Aurelius (and Lucius Verus). This merit-first chain brought unusual stability and prosperity at the height of the Pax Romana. It ended when Marcus Aurelius named his biological son Commodus.

Memory tip: “Adopt, don’t inherit.” In elite Roman society, adoption was a standard tool for passing on name, property, and power—more like designating a capable heir than modern family adoption. Not primogeniture or election, but chosen heirs through adoption.