While the borrowing of techniques between hagiographers and romance writers throughout the Middle Ages has been well established, scholars generally discuss the nature and purpose of such borrowing as if they remained constant through several centuries, explaining the "purpose of saints' lives", as if it had never changed. Dr. Smith argues that explanations that served for the thirteenth century, when the Church was at the height of its power and the feudal system functioned well, do not serve for the fifteenth century, when both were in decline. In the literature of thirteenth- through fifteenth-century England, the genres of hagiography and romance developed like children of the same family. Their resemblance is undeniable, their relationship important, but troubled. The earliest hagiography, composed in late antiquity and the early Middle Ages, consists mostly of stories about martyrs of the early Church. Because the canonical status of a saint depended upon his making the ultimate sacrifice for the faith, as well as the miracles he performed before and (especially) after his death, the most important part of a saint's life was considered to be his martyrdom, or passion.
In the later Middle Ages, when holy men and women who were not necessarily martyrs became eligible for sainthood, hagiographers began to include other events, such as the saint's conversion, divine visions, or mystic marriage. Eventually, such stories about saints' earlier lives, called vitae, became more attractive to both readers and writers than the passions. Saints' lives, in both forms, were exceedingly popular throughout the Middle Ages, at least as popular as the romances about knights and their adventures with which modern audiences are more familiar.