The Shards of Narsil were what was left of the broken sword Narsil.
In the NovelsEdit
In The Fellowship of the Ring, they are carried by Strider. He uses the fact that he is carrying "the blade that was broken," mentioned in All that is Gold Does Not Glitter in Gandalf's letter, to try to convince Sam Gamgee that he is truly Aragorn. The shards are also mentioned in the poem Seek for the Sword that was broken that Boromir and Faramir hear in their dreams. In the book, the shards are reforged at Rivendell before the Fellowship of the Ring leaves, and Aragorn renames the sword Andúril.
In the MoviesEdit
In The Hobbit: An Unexpected Journey (extended version), 60 years before the events of the Lord of the Rings, Bilbo notices the shards on display, before seeing the painting of Sauron and Isildur during the War of the Last Alliance between Elves and Men.