A mandala, meaning circle, is a graphic, geometric representation of the universe with a deity's palace at the centre used to support meditation. Usually a mandala takes the shape of an elaborate 4-gated city where the practitioner enters, approaching the centre to achieve a state of mystical unity with Buddha. Each object in the palace has significance, representing some aspect of wisdom or reminding the meditator of some guiding principle. The Kalachakra Mandala, Avalokiteshvara Mandala, and Chakramsamvara Mandala are some of the most common mandalas.