Prince Caspian Must Flee
"Shall I never see you again?" said Caspian in a quavering voice.
"I hope so, dear King," said the Doctor. "What friend have I in the wide world except your Majesty? And I have a little magic. But in the meantime, speed is everything. Here are two gifts before you go. This is a little purse of gold alas, all the treasure in this castle should be your own by rights. And here is something far better."
He put in Caspian's hands something which he could hardly see but which he knew by the feel to be a horn.
"That," said Doctor Cornelius, "is the greatest and most sacred treasure of Narnia. Many terrors I endured, many spells did I utter, to find it, when I was still young. It is the magic horn of Queen Susan herself which she left behind her when she vanished from Narnia at the end of the Golden Age. It is said that whoever blows it shall have strange help - no one can say how strange. It may have the power to call Queen Lucy and King Edmund and Queen Susan and High King Peter back from the past, and they will set all to rights. It may be that it will call up Asian himself. Take it, King Caspian: but do not use it except at your greatest need. And now, haste, haste, haste. The little door at the very bottom of the Tower, the door into the garden, is unlocked. There we must part."
~C.S. Lewis, Prince Caspian, (1951)