Alcuin wrote his De fide sanctae Trinitatis et de Incarnatione Christi in 802, as Charlemagne was concluding his decades-long war in Saxony. Considered by many to be Alcuins masterpiece, the De fide was one of the most widely read and circulated works in the entire Alcuinian corpus; today it survives in 100 medieval manuscripts. Alcuin wrote specifically to provide guidelines for the catechetical instruction of pagan Saxons. His short treatise thus provides rare, direct evidence for the content of early medieval missionary preaching. Together with several companion texts, including a credal statement, a litany, and a series of questions and answers addressed to Alcuin's pupil Fredegisus, the De fide sheds light on a wide range of Carolingian-era theological preoccupations, with discussions on topics as diverse as the procession of the Holy Spirit, the Incarnation, the two natures of Christ, and the resurrection of the body.