"How did it happen that such masses heeded the voice of God, left their wives, relatives, estates?" - asked Fulchery of Chartres, a participant and chronicler of the First Crusade. And in fact, what forced thousands and thousands of people to leave their homes and with weapons in their hands to go on incredible overseas pilgrimages, from which many were not destined to return? Who were they, the leaders and ordinary participants in the crusades, who carried with them not only love for God, but also death and destruction - mad fanatics, adventurers eager for enrichment, warriors, doing their duty with pure thoughts, or ordinary people who fell into the cycle of religious enthusiasm? And how did it arise for the first time and why was the wave of crusading enthusiasm repeated more than once, raising entire peoples on the road - and in general, what was it? Olga Dobiash-Rozhdestvenskaya's book answers these questions.