Like the kings, dignitaries and village chiefs also erected memorial altars to their deceased predecessors. Ritual sacrifices at these altars strengthened the relationship between the living and their ancestors. The furnishings of the altars are comparable to those of the royal memorial altars. The decisive difference lies in the use of certain materials that were an expression of Benin's hierarchical society. Brass for memorial heads and altar figures or ivory were, with a few exceptions, reserved for the king. On the memorial altars of people of lower rank were memorial heads made of wood, some of which were covered with thin sheet brass as an expression of special privilege on the part of the king.