The Arkenstone was considered to be the greatest treasure of all the Dwarf-hoards. It is also called the Heart of the Mountain, or the Arkenstone of Thráin. The jewel was lost, that is left behind, in Erebor during Smaug’s attack on Erebor. Not much is known about the Arkenstone, but the corruption it caused was visible in Thorin Oakenshield, who almost killed his friend Bilbo Baggins, for taking the Arkenstone to Thranduil and Bard the Bowman, in an attempt to reconcile two sides and prevent the Battle of the Five Armies. His attempt failed, and Thorin makes Bilbo leave Erebor. The Arkenstone was buried with Thorin Oakenshield after he died of the wounds suffered in the battle, since he was the King under the Mountain, even for a short while.