From the Catholic Encyclopedia:
The hymn in praise of the paschal candle sung by the deacon, in the liturgy of Holy Saturday. In the missal the title of the hymn is "Praeconium", as appears from the formula used at the blessing of the deacon: "ut digne et competenter annunties suum Paschale praeconium . Outside Rome, the use of the paschal candle appears to have been very ancient in Italy, Gaul, Spain, and perhaps, from the reference by St. Augustine (City of God XV.22), in Africa. The Liber Pontificalis attributes its introduction in the local Roman Church to Pope Zosimus. The formula used for the "Praeconium" was not always the "Exultet", though it is perhaps true to say that this formula has survived, where other contemporary formulae have disappeared. In the "Liber Ordinum", for instance, the formula is of the nature of a benediction, and the Gelasian Sacramentary has the prayer "Deus mundi conditor", not found elsewhere, but containing the remarkable "praise of the bee — possibly a Vergilian reminiscence — which is found with more or less modification in all the texts of the "Praeconium" down to the present day. The regularity of the metrical cursus of the "Exultet" would lead us to place the date of its composition perhaps as early as the fifth century, and not later than the seventh.
