A barrier comprising a base unit composed of a bullet resistant material and a transparent upper wall removably interconnected to the base unit and composed of a bullet resistant material. The base unit includes a front wall and two side walls extending from the front wall to provide protection to the front and sides of a person standing behind the barrier. A series of casters, preferably locking casters, are attached to the bottom edges of the side walls, and a pair of handles connected to each of the side walls permitting the barrier to be conveniently transported from one site to another.