The Crusades has been presented as an era of unremitting holy war and religious violence that is often seen as the origin of the supposed “Clash of Civilizations” that characterizes Islamic-Christian-Jewish relations. Religious studies Professor Brian Catlos will look at the causes and contexts of the Crusades for a provocative retelling of the history of this complex era. Saturday, Jan. 30, 1 to 3 p.m., Butcher Auditorium, Biotechnology Building. The presentation is part of CU on the Weekend, which is free and open to the public.