Mark, as usual, amplifies. Matthew has simply the Pretorium. The courtyard, surrounded by the buildings of the Pretorium, so that the people passing through the vestibule into this quadrangle found themselves in the Pretorium.
Band (σπεῖραν)
Originally anything wound or wrapped round; as a ball, the coils of a snake, a knot or curl in wood. Hence a body of men-at-arms. The same idea is at the bottom of the Latin manipulus, which is sometimes (as by Josephus) used to translate σπεῖρα. Manipulus was originally a bundle or handful. The ancient Romans adopted a pole with a handful of hay or straw twisted about it as the standard of a company of soldiers; hence a certain number or body of soldiers under one standard was called manipulus.