The Medieval Church · c. 1195–1197
On the Sacred Mystery of the Altar
De Sacro Altaris Mysterio
Innocent III · 1160/61–1216
What it is
A detailed commentary on the mass, its vestments and gestures, written before its author's election and used as an authority long after.
Why it lasted
The most influential papal treatment of the eucharist before the Fourth Lateran Council defined transubstantiation.
Where to read it
This work is in the public domain and can be read in full, free, at the archives below. The Library catalogues it; it does not host the text.
These open a search on each archive rather than a direct link, which is the honest way to point at an edition nobody here has checked line by line.
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