Breastfeeding is the natural means by which a baby receives nourishment. In most societies women usually nurse their own babies, this being the most natural, convenient and cost-effective method of feeding a baby. However, there are situations when a mother cannot suckle her own baby. For example, she may have died, become unwell or otherwise cannot produce breast milk. Before the availability of infant formula, in those situations, unless a wet nurse was found promptly, the baby might die, and infant mortality rates were high. Wet nurses were a normal part of the social order, though social attitudes to wet nursing varied, as well as to the social status of the wet nurse. Breastfeeding itself began to be seen as common; too common to be done by royalty, even in ancient societies, and wet nurses were employed to breastfeed the children of royal families. This attitude extended over time, particularly in western Europe, where babies of noble women were often nursed by wet nurses. Lower-class women breastfed their infants and used a wet nurse only if they were unable to feed their own infant.