In ancient times, tribal nations preferred endogamous marriage marriage to one's relatives; the ideal marriage was usually that to a cousin, and it was often forbidden for an eldest daughter to even marry outside the family. Marriage to a half-sister, for example, is considered incest by most nations today, but was common behaviour for Egyptian pharaohs; similarly, the Book of Genesis portrays Sarah as marrying Abraham, her half-brother, without criticising the close genetic relationship between them, and the Book of Samuel treats the marriage of a royal prince to his half-sister as unusual, rather than wicked.