“Yeah, but the lost diadem is lost… that’s sort of the point.”
—Michael Corner to Luna Lovegood
Ravenclaw’s Diadem (also known as the Lost Diadem of Ravenclaw) was the only known relic once belonging to Rowena Ravenclaw, the founder of Ravenclaw House at Hogwarts School of Witchcraft and Wizardry. Etched upon its surface was Ravenclaw’s famous quote: “Wit beyond measure is man’s greatest treasure.” It was said to enhance the wisdom of its wearer, which is Ravenclaw House’s most treasured attribute. It has a blue sapphire shaped like an oval. The diadem was later stolen by her daughter, Helena, a fact Rowena kept a secret from the other founders ’till her death bed.
Rowena Ravenclaw’s Diadem, Helga Hufflepuff’s Cup and Salazar Slytherin’s Locket, made up three of Lord Voldemort’s Horcruxes.