This article highlights the imperative of building defences of peace in the human mind, articulated in the Constitution of UNESCO. Pursuing the question of how such defences can be built in contexts of religious antagonism, the article explores the work of ecumenical theologians who seek to find ways of building defences of peace in the minds of believers. The exploration involves intersecting ecumenical theology with the fields of religious education, cognitive science, and peace studies. In this way, the article brings introductory perspectives to interdisciplinary research that considers pressing questions of how to overcome violence and build peaceful communities. Throughout the investigation, hope and imagination serve as guiding concepts. Hope is discussed with regard to memory, change of perceptions, and the building of trust and peace. However, the article also considers the tendency towards constructing imagined enemies. Elucidating how empathetic imagination can provide resistance to this tendency, it discusses the way dialogue might break destructive habits of imagining the religious other as an enemy. With a view to this capacity of dialogue, the article considers the role of longstanding endeavours of ecumenical exchange in processes towards overcoming violence and constructing defences of peace in human minds.