With kings and emperors, a big problem is the order of succession. Kings were sometimes followed by their eldest son, if he was capable of ruling. For Roman emperors, more often it would be an adopted son. It worked like this. The emperor would notice an outstanding young man from one of the best families. He would adopt him as his son. Before he died he would make clear whom he thought should succeed him, by making him a Roman consul, or by stating in his will that the younger man should succeed him. Sometimes this worked; sometimes it did not. Every now and then there would be a civil war between claimants to the throne.