The religious developments of the European Middle Ages (c. 400-1500), including popes, religious orders, heresies, and more.  Main source is Bennett, 'Medieval Europe: A Short History'.  (Note that this timeline is best used in conjunction with the Medieval Europe Politics and Culture timelines, as the distinctions between these three spheres are in many cases more or less arbitrary.  Furthermore, these timelines are mostly intended for those who have some sense of the period already, but want a little refresher; commentaries may be more or less helpful).  Some dates may be approximate.