The crusade is phenomenon popularly attractive. There is much written about it, and even more spoken. With this presentation we only pretend to focus the theme of the traditional meaning of the crusade, the one that we have named the first crusade, the reference over which the following ones are measured. This way, it is this first crusade experience the one that allows us approaching in a better way to the richness of concepts and realities that are hidden behind it. And for this, we will try to have a better knowledge of the possible intentions and comprehend the phenomenons that its own protagonists were. In this sense, the papal speech of Clermont -in which, by the way, the word 'crusade' is not pronounced, simply because it was born much later than the capture of Jerusalem- offer us fundamental keys.