Theologische Realenzyklopädie: Band 20 Kreuzzüge - Leo XIII.

The Theologische Realenzyklopädie (TRE) [Theological Encyclopedia] is a modern specialist encyclopaedia comprising 36 volumes of text (1976–2004) representing the present state of theological research as a whole. More than a generation of scholars have collaborated in its production, to create a unique internationally-oriented reference work containing more than 2, 500 articles (on over 28, 000 pages of text) which stands as a document of the history of scholarship. The TRE is an indispensable tool for research, study and teaching, principally in theology, but also in its neighbouring disciplines such as history, philosophy, Jewish studies and religious studies.

TRE is also available as paperback edition
Aaron - Katechismuspredigt (17 volumes)
Katechumenat/Katechumenen - Publizistik/Presse (10 volumes)
Pürstinger - Zypern (9 volumes)
Gesamtregister (Bibelstellen, Orte, Sachen, Namen - 2 volumes)

Further there is an online resource Theologische Realenzyklopädie Online.