The heirloom arrow with which Bard the Bowman slew Smaug.

Bard inherited the Black Arrow which was fletched for one of his ancestors in Dale by the King under the Mountain. It had been used many times, but was always retrieved, until its final flight into Smaug’s breast. Bard’s words to it as he fitted it to his bow-string imply that the death of Smaug was its destiny.

Editor’s Note: The Black Arrow is one of several weapons in Middle-Earth destined to fulfil themselves in a particular event. Swords and knives being the most obvious. Frequently the weapon, though much used and of some antiquity, fractures, dissolves or is otherwise destroyed at the culmination of its fate.
Encyclopedia entry originally written by cirdaneth