The 20th-century liturgical movement grew in tandem with the biblical, ecumenical, ecclesiological, and patristic movements, all part of a wider movement of resourcement—a return to biblical and patristic sources. Indeed, the success of the liturgical movement in the 20th century, ultimately ratified in the liturgical reforms of the Second Vatican Council (1962–1965), can be seen precisely in its collaboration with those other ecclesial movements for church reform. Especially important was the ecumenical liturgical cooperation that grew across denominational lines as the movement took shape in different churches. Belgian Benedictine Lambert Beauduin (d. 1960) of Mont César is considered the founder of the Roman Catholic liturgical movement; during a national Catholic labor conference, held in Malines in September 1909, he delivered a conference on the liturgy as the “true prayer of the Church.” Taking his cue from Pope Pius X’s 1903 motu proprio “Tra le sollecitudini,” in which he spoke of the liturgy as “the true and indispensible source” for the Christian life, Beauduin argued that liturgy was foundational for Christian mission and social outreach. This message was consistent with the parish communion movement within the Church of England at the dawn of the 20th century and, indeed, in what the founder of the liturgical movement within the Church of England, A. Gabriel Hebert, S. S. M., wrote in his classic 1935 text Liturgy and Society. In Germany, the movement centered on the Benedictine monastery of Maria Laach and was more scientific in scope. Soon the movement took hold in Austria, France, and the rest of Europe, as well as in the Americas, in Anglican, Lutheran, and Roman Catholic churches in particular. It is precisely because of this common return to the sources that the 20th-century liturgical movement can only be understood in its wider ecumenical context.