The crown of Alderaan was the official crown of the Alderaanian monarch. It was normally kept in a museum, but was occasionally displayed in the royal palace's throne room on special occasions, such as the heir's Day of Demand.
In 27 BBY, when Alderaan's queen Breha Organa greeted Senator Padmé Amidala and her entourage in the palace throne room she had the crown woven into the braid that was twisted up into the top of her head.
In 3 BBY, the crown was brought back from the museum to the palace throne room for Princess Leia's Day of Demand. The crown was placed upon a marble pillar and illuminated by its own candledroid.