Medieval Christian theology places seraphim in the highest choir of the angelic hierarchy. They are the caretakers of God's throne, continuously singing "holy, holy, holy". Pseudo-Dionysius the Areopagite in his "Celestial Hierarchy" (vii), drew upon the Book of Isaiah in fixing the fiery nature of seraphim in the medieval imagination. Seraphim in his view helped the Deity maintain perfect order and are not limited to chanting the "trisagion". Taking his cue as well from writings in the Rabbinic tradition, the author gave an etymology for the "Seraphim" as "those who kindle or make hot"