Such were the birrus (so-called from its red colour), abolla and lacerna.
There is some difference of opinion as to the derivation of the vestment in the latter case; the Five Bishops (Report to Convocation, 1908) deriving it, like the cope, from the birrus, while Father Braun considers it, as well as the cope, to be a modification of the paenula.'
Moreover, it would be further necessary to prove that the birrus, in contradistinction to the paenula, was always open in front; whereas, per contra, the paenula, both as worn by soldiers and in ordinary life, was, like the modern Arab burnus, often slit up the front to the neck.
Their statement, however, that it is "pretty clear" that the cope is derived from the Roman lacerna or birrus is very much open to criticism.
We do not even know what the appearance and form of the birrus were; and the question of the origin of the cope is not whether it was derived from any garment of the time of the Roman Empire, and if so from which, but what garment in use in the 8th and 9th centuries it represents.