Manuscript ALC-34 in the Biblioteca Nacional de Portugal de Lisboa (Lisbon) is a collection of theological texts from the cistercian abbey of Alcobaça. (Originally shelfmark CCXXXVIII in the abbey library.)
At the back of the volume was a parchment folio with musical notation, dating from the end of the 13th century or beginning of the 14th, which had been repurposed as a combination of flyleaf and pastedown. It has since been removed from this context and is preserved by the library separately as ALC-34/1.
This fragment contains three two-part motets from the Ars Antiqua repertory, all of which can be found nearby one another in the Medici Antiphoner (F), and one of which can be found in the Las Huelgas and Madrid codices.
The current recto (corresponding to the recto side of its use as a flyleaf) was the original verso, and vice-versa (the motet Alta bovi et leoni aquile begins on the current verso and continues to the current recto). Both sides were evidently ruled with six red 5-line staves (there is no gap in the text and music for the above motet), the topmost of which has been cropped, along with the original outside margin.