The Biretta is a square cap with three ridges or peaks on its upper surface. It is worn by clerics from cardinals to seminarians. The use of such a cap is prescribed by the rubrics both at solemn Mass and in other ecclesiastical functions. The origins of the biretta are uncertain. It is mentioned as early as the tenth century. One possible origin is the academic cap of the high Middle Ages, which was soft and square.
The biretta seems to have become a more widely used as an ecclesiastical vestment after the synod of Bergamo, 1311, ordered the clergy to wear the “bireta on their heads after the manner of laymen.”The tuft or pom sometimes seen on the biretta was added later; the earliest forms of the biretta did not bear the device.
The Bishop’s biretta is a hard square cap. For a bishop, it is purple in color with a pom of the same color as the biretta. A bishop on the inside of a church uses the biretta, when he is not in vestments. Priests’ birettas are black with a pom, while Seminarians and Deacons’ are black with no pom. In addition, Cardinals have red birettas with no pom.
The priest (Bishop, Cardinal or Seminarian) all wear the Biretta outside of Mass. In the extraordinary form of the Mass (Traditional Latin Mass) the priest is required to wear a biretta which he wears processing up to the altar, during the homily and for the procession out of Mass. The priest also wears the biretta outside of the church in the public eye as another piece to his “clerical garb.”
The different times that clergy wear their birettas is due to the importance of what is taking place in front of them (and for priests) in them. At Mass the priest acts in persona christi, so it is only fitting that the priest “opens up himself” symbolically through the removal of the biretta. In this action he loses himself and his humanity and Christ takes over as the priest-victim. Then when Mass is over the priest enters back into his second identity as the priest-human which is symbolically shown in the use of the biretta.