Balthasar goes to Mantua to deliver Romeo's message about Juliet's faked death, in order to prevent Romeo from committing suicide when he hears the news of her death.
Balthasar.
Romeo commands Balthasar to prepare his horse and deliver a letter to his father in Mantua. He instructs Balthasar to not return to Verona or inquire about Juliet's condition.
Balthasar brings Romeo the news of Juliet's "death"
Balthazar.
At the beginning of the act, he is in Juliet's bedchamber before he goes into exile in Mantua for the rest of the act.
He goes to Mantua.
He isn't banished anywhere he is banished from his town that he is currently living in. Meaning he can go anywhere else. *He is banished to Mantua
Friar Laurence advises Romeo to go to Mantua and wait for news of when it is safe for him to return to Verona.
In Act 5 scene 1, Romeo's servant Balthasar arrives in Mantua to bring Romeo news from Verona. He tells Romeo that Juliet was found dead that morning.
Balthasar heard that Juliet had died. Balthasar went to Mantua, where Romeo was, because Romeo was banished from Verona for killing Juliet's cousin-> Tybalt. Romeo heard from Balthasar that Juliet was dead en he rushed to Verona, to Juliet's tomb. The letter that Friar Lawrence sent to Romeo to warn him that Juliet was in fact not dead at all, came to late-> Romeo already left to see his beloved Juliet for the last time
Mantua
Mantua :)