 He's always kept her in a cage because she's never been able to do anything up until this point for herself. And this is where he makes his very big mistake, I think, which is that his heirs are still too young. He adopted them as babies and the oldest one is only six when Agrippa dies. He still needs a son-in-law to be a real heir if he dies in the next couple of years. And so he forces Julia to marry his stepson, Tiberius.