A famous example of this custom is Julius Caesar's adoption of his great-nephew, Gaius Octavius. Primogeniture is notably absent in the history of the Julio-Claudian dynasty. Augustus, Caligula and Nero failed to father biological and legitimate sons.
Julio-Claudian dynasty, (ad 14–68), the four successors of Augustus, the first Roman emperor: Tiberius (reigned 14–37), Caligula (37–41), Claudius I (41–54), and Nero (54–68). It was not a direct bloodline.
The Julio-Claudian Dynasty (27 B.C.–68 A.D.)
Claudius, in full Tiberius Claudius Caesar Augustus Germanicus, original name (until 41 CE) Tiberius Claudius Nero Germanicus, (born August 1, 10 bce, Lugdunum [Lyon], Gaul—died October 13, 54 ce), Roman emperor (41–54 ce), who extended Roman rule in North Africa and made Britain a province.