According to the tale of the Deathly Hallows, the Peverell brothers challenged Death, who then gave them a choice of anything they wanted. The first brother chose a wand (The Line) that could not be defeated in battle. The second brother asked for a way to bring someone back from the dead; he was given the Resurrection Stone (the Circle). The third brother selected a cloak that made the wearer invisible, even to Death himself (The Triangle.)
Combined, these symbols create a powerful amulet. Wear this pendant on all of your adventures!