Horatio: That can I; At least, the whisper goes so. Our last king,
Whose image even but now appear’d to us,
Was, as you know, by Fortinbras of Norway,
Thereto pr*ck’d on by a most emulate pride,
Dar’d to the combat; in which our valiant Hamlet—
For so this side of our known world esteem’d him—
Did slay this Fortinbras; who, by a seal’d compact,
Well ratified by law and heraldry,
Did forfeit with his life all those his lands
Which he stood seiz’d of, to the conqueror;

What is the main purpose of Horatio’s speech?

to describe to the audience the location of the castle and kingdom
to help the audience better understand Horatio’s character
to inform the audience of the events leading up to this point
to explain to the audience how the former king died and became a ghost