The ring that belonged to the father of Marcus is now in the possession of an old Celtish war lord named Tradui. When Marcus travels past Hadrian's Wall in order to try and refind the eagle of his father's regiment and regain honour for both himself and his father, his disguise allows him to befriend Tradui and to be shown the ring that Tradui took from his father when he and his tribe of men had killed the Roman regiment. Note how the ring is introduced:
A ring swung on the end of the thong, sparkling faintly with green fire in the torch-light. Marcus took it from him and bent his head to examine it. It was a heavy signet-ring; and on the flawed emerald which formed the bezel was engraved the dolphin badge of his own family.
This section of the novel is significant, because not only does Marcus find out finally what happened to his father, he also is given proof in the form of the ring that what Tradui tells him is true. It is later in the novel in Chapter 19, that Tradui sends Liathan, one of his warriors, to give the ring to Marcus; either to bury it with him if he is killed or to hand it over. Marcus is thus reunited with his father's ring, which is of course tremendously meaningful to him.