Which one of the eight most ancient Christian Hymns requires the first letter to be capitalized?
Rosary:  When used of the form of prayer, the word is usually capitalized ("the Rosary"), as is customary for other names of prayers, such as "the Lord's Prayer", "the Hail Mary", "the Magnificat". Magnificat: The Magnificat (Latin: [My soul] magnifies [the Lord] ) is a canticle, also known as the Song of Mary, the Canticle of Mary, and, in the Byzantine tradition, the Ode of the Theotokos (Greek: Ἡ ᾨδὴ τῆς Θεοτόκου ). Magnificat:  It is one of the eight most ancient Christian hymns and perhaps the earliest Marian hymn.
The Magnificat