Susan's Horn
From WikiNarnia, the Narnian Encyclopedia
The Horn of Queen Susan Pevensie of the Kingdom of Narnia was a magical hollowed ivory animal horn used in times of emergency to call for help. It was given to Susan by Father Christmas just before the Winter Revolution, who said if it was blown, help would always come.
Susan first used it when she was attacked by Maugrim the wolf as the Battle of Aslan's Camp was about to break out. Peter heard it and saved her life. The sound of it was described as "like a bugle, but richer".
Queen Susan took the horn with her to Lantern Waste during the hunting of the White Stag, and after the children returned through the wardrobe portal the horn became lost for many years. Eventually it was found by half-dwarf Doctor Cornelius. Shortly before the Narnian Revolution Cornelius passed the horn to Caspian X. The legend of its magical ability to summon aid was known to Cornelius, and during the siege at Aslan's How, after much debate, Caspian blew it. It had the effect of magically transporting the Pevensies back to Narnia. However they didn't appear at the location of the horn, at Aslan's How, but at Cair Paravel.
Later when Caspian set out on his voyage on the Dawn Treader he gave the horn to his regent Trumpkin to use if any great need fell on the land in the king's absence.
The horn then came lost for the rest of the years to come after the last battle
