HIEROS (in ancient Greek: sacred), performed by the vocal trio of the Céladon ensemble, opens a musical reflection that alternates between medieval music and contemporary composition. With this first entirely a cappella sung album, the ensemble led by Paulin Bündgen questions the definition of the "sacred" and its evolution from yesterday to today. From the conductus of the Notre-Dame School of the 13th century to the 6 works by Jean-Philippe Goude, how has this feeling, which inhabited and guided the artists of the Middle Ages, evolved? What meaning and what place does our modern world give it? As often, the answer is tangible when it is formulated in music.