While bells and rattle staffs are placed on all ancestral altars, ivory tusks and commemorative brass heads are made specifically for royal altars. Associated with trade, ivory and brass are durable and valuable, and their colors—white like sacred kaolin clay and red like fire and coral beads—relate to royal power. Before the British conquest, an oba's courtyard was the focal point for rituals in his honor. British troops reported 18 altars dedicated to previous obas when they took possession of the palace in 1897. Today, all of the royal altars stand together in a single courtyard. One of the objects unique to Benin art is an Ikegobo, or "altar to the hand," which celebrates the accomplishments of exceptional individuals. The hand is associated with action and productivity, and is considered the source of wealth, status, and success for all those who depend on manual skill and physical strength. Altars of this kind are commissioned in terracotta, wood, or brass, depending on the status of the patron. Private and public ceremonies mark many of the important moments in Benin's yearly calendar. In the past, an elaborate series of rites were performed throughout the year to secure otherworldly support for the kingdom's well-being and to celebrate decisive events in its history. For the sake of convenience, the current monarch, Oba Ewuare II, emphasizes the end-of-year festival called Igue, which is held during the winter holidays to allow the greatest number of people to attend. Igue includes a sequence of rituals that renew the oba's supernatural powers and cleanse the kingdom's unruly spirits. Benin's other important ritual festivals include Ague, where the first budded yams are blessed in hopes of a successful harvest; Ugie Ivie, the Festival of Beads, in which the oba's coral and red stone regalia is bathed in cow's blood to reinvest it with spiritual force; Ugie Erha Oba, which honors the oba's father and all paternal ancestors; Oduduwa, a masquerade that likewise honors the oba's paternal ancestors; and Ugie Oro, celebrating Oba Esigie's victory over the Idah Kingdom in the 16th century. Finely carved ivory double gongs are examples of art related to rituals at court. They are called “double” gongs because of second, smaller resonating cups at their front. Typically, the central image is the oba in coral regalia supported by the high priests osa and osuan, officials who tend the altars of the kingdom's two patron gods.