Ivory money comes in various forms and sizes: as full tusks, as spans (sections), disks and rings. In West Africa it was until recently money of the chiefs, as commoners were not allowed to have ivory in their possession without the chief's approval. Its value was due to the knowledge required and difficulty involved in the killing of elephants and the cutting of their tusks. For Europeans, slaves and ivory were the two most important and desired African items. Their value was accordingly high. In the 19th century, a pair of tusks paid for room and board of an entire caravan.