Yep, it's a PBEM, there are two other human players. They're not really participating in the thread, if only because they think it would give them an unfair advantage. I don't mind if they peek, though, because Otho is so powerful that they need some sort of help.
Seeing as they don't know about this thread, I can lay out my real strategy. I'm just doing massive naval patrols and a little bit of cavalry spying on Vespasian; I'm not interested in fighting him anytime soon. Most of my army is heading north to destroy Vitellius. I honestly hope Vitellius is not coming down south to avoid the Alps, because right now the bulk of my force is crossing the Alps to confront that army that's sieging me. If he does come around south, then he'll only be opposed by about 4 units of Auxiliaries, and whatever local militia I can summon.
Next turn two armies will arrive about a province away from the siege, and then the turn after that they will both come marching in to break the siege and route the northerners. Once that occurs, I will march a single army slowly north, sieging and taking provinces as I go. The rest of my army will head back across the Alps into Italy and I'll figure my next move.
If I do another PBEM after this I'll let you know. I'm actually pretty bad at this game, though.