In that case the celebrant stood behind the altar at mass, and looked over it eastwards towards the people.
Whenever a bishop was celebrant he was to wear, "beside his rochette, a surplice or albe, and a cope or vestment," and also to carry " his pastoral staff in his hand, or else borne or holden by his chaplain."
The object of the change was primarily to leave the hands of the celebrant freer for the careful performance of the manual acts, and to this end a process of cutting away at the sides of the vestment began, which continued until the tent-shaped chasuble of the 12th century had developed in the 16th into the scapular-like vestment at present in use.
But in the middle ages the altars were placed against the east wall of the churches, or else against a reredos erected at the east side of the altar, so as to prevent all access to the table from that side; the celebrant was thus brought round to the west side and caused to stand between the people and the altar.
Hitherto the chasuble had been worn indifferently by all ministers at the eucharist, even by the acolytes; it had been worn also at processions and other non-liturgical functions; it was now exalted into the mass vestment par excellence, worn by the celebrant only, or by his immediate assistants (deacon and subdeacon) only on very special occasions.