The Codex Calixtinus was created in the 12th century as a guide for visitors on the Camino de Santiago. It contains sermons, liturgical texts, a guide to the route, and other sections
Among the additional material of interest is a narrative of the Charlemagne's campaign in Spain and the battle of Roncevaux. This text describes the events more famously narrated in the Chanson de Roland. This section was physically separated from the other parts of the manuscript in the 17th century.
The Codex also contains 22 examples of medieval polyphony, making it an important early source. The most notable single work is Congaudeunt Catholici believed by some musicologists to be the earliest extant example of three-part music. audio 
The manuscript is housed at Compostella. It was stolen in 2011 and found by police in 2012 in the garage of a disgruntled former cathedral employee.