Obtained: Automatically after completing The Common Thread main goal and is tied to A Herculean Task
Objective: Find the Roman plaque
Ask Rufius about the Roman plaque
Speak with Rufius and ask him about the Roman plaque. Encourage him by reminding him that you helped treat his rheumatism (if you completed A Thorn in the Paw lead). He’ll give you a Key to the Secret Shrine.
Ask Malleolus about the Roman plaque
If you ask Malleolus about the plaque, he’ll say that if he had it, he would sell it to you. If you kill him, you will be able to loot the shrine key from his body. With the key in hand, make your way to the amphitheater (left of the baths) and follow the path through an old archway. Keep heading forward, sticking to the right path. This will bring you to down a set of stairs and to a torch on the right just before a barrel. You want to take the narrow path just past the barrel, which will lead you to the locked shrine. Use the key to open the door then grab the Roman plaque from the table.
Ask Octavia about the Roman plaque
You can ask her about it but she will refuse to tell you where it is even if you try to blackmail her about her religion.
Figure out a way into the locked shrine
For this one, you’ll need the golden bow. Enter the tavern and head to the other side of the room across from Aurelia at the bar. Work your way past a pedestal with a gold statue on it then head through the doorway. Take a right and head up the stairs following the path left. This will bring you to a wooden shack in a cave. Keep moving past the shack then take next right and continue following the path forward. At this point you should have went up a hill and entered a part of the cavern with five golden statues. Head forward a little farther to reach a wall with vines growing down it. Shoot the vines with the golden bow then climb up it. Drop down in the locked shrine area below to find the Roman plaque on the table.