Why is it canonical?

In addition to representing the influence of Gothic architecture in Italy, epitomized in France by Clairvaux and spearheaded by the work of the Cistercian order, Fossanova represents the spare and simple style of the Cistercians that strongly resonated with the mendicant orders (the Dominicans and Franciscans) that emerged in Europe and Italy especially around the time of Fossanova's construction. As a result, Fossanova not only stands as a continuation of a trend throughout Europe by the beginning of a new trend in architecture, worldview, and desire for reform carried forward by the mendicants.