The legacy of Safiy a-d-Din al-Urmawi ( -1294) is crucial for the knowledge of the medieval Arab musical tradition. The purpose of this paper is to study the instrumental and vocal corpus of the Book of Cycles, as written by al-Urmawi according to an original alphabetical and numerical system of musical notation. This small repertoire represents the only Arabic musical heritage that scripturally outlasted after the fall of the Abbasids. The paper starts with a critical rereading of the theoretical musical system of al-Urmawi, aiming at redefining its effective intervallic structures. Then this melodic and modal hermeneutics, combined with an analysis of the rhythmic modules, is used in order to allow the paleography to operate in the prospect of a musical transcription and a revivification that tries to reach equilibrium between the requirements of historical musicology and those of the live tradition.