Agnus Dei Introdcution and Changes Made in History of the Church Regarding Agnus Dei

According to the Liber pontificalis Pope Sergius I (687- 701) introduced the Agnus dei into the Roman Mass

Agnus dei qui tollis peccata mundi, miserere nobis.
Agnus dei qui sedes ad dexteram patris, miserere nobis.
Agnus dei qui tollis peccata mundi, miserere nobis.

Lamb of God, who takes away the sins of the world, have mercy on us.
Lamb of God, who sits at the right hand of the father, have mercy on us.
Lamb of God, who takes away the sins of the world, have mercy on us.

Around the year 1000 the Agnus dei assumed the textual form that eventually became standard throughout the Roman rite:

Agnus dei qui tollis peccata mundi, miserere nobis.
Agnus dei qui tollis peccata mundi, miserere nobis.
Agnus dei qui tollis peccata mundi, dona nobis pacem. (Lamb of God....grant us peace.)