As Marcius had expected, the bastards from the Order of Purple Sun retaliated. And Marcius was fine with it
In fact, Marcius was counting on it to happen.
If the party getting arrested with criminal charges for breaking the law of the High King and the Solas church did not resist the arrest, it would not paint a very bad picture for them. Many would just think that it would just be a misunderstanding and would shrug off the event. Well, if the party getting arrested resisted, however, it would paint a picture that the Order of Purple Sun indeed had secrets to hide - possibly their illegal activities.
Now, the bastards had resisted arrest in the worst way possible. They started the hostile interaction by attacking first. And, not only did it shine a bad light on the people of the order within the walls of Mediolan in a bad light, but now Marcius and his troops would also have a very good reason to go in, gun blazing.