"The Letters of a Portuguese Nun" by Guilleragues is a work of epistolary fiction first published in 1669. Five passionate letters form a haunting monologue of love, progressing through desire, faith, doubt, and despair toward a tragic conclusion. Originally attributed to a Portuguese nun writing to her French lover, the work became a European sensation and sparked debates about authenticity that persisted for centuries. These letters revolutionized European literature, establishing a template for sentimentalism and inspiring the epistolary novel tradition that flourished throughout the eighteenth century. (This is an automatically generated summary.)