Many archaeologists argue that the ancient authors and the evidence of the Tophet indicates that all remains in the Tophet must have been sacrificed. Others argue that only some infants were sacrificed. Paolo Xella argues that the weight of classical and biblical sources indicate that the sacrifices occurred. He further argues that the number of children in the tophet is far smaller than the rate of natural infant mortality. In Xella's estimation, prenatal remains at the tophet are probably those of children who were promised to be sacrificed but died before birth, but who were nevertheless offered as a sacrifice in fulfillment of a vow. He concludes that the child sacrifice was probably done as a last resort and probably frequently involved the substitution of an animal for the child.