Abstract: A protective grille assembly mountable over a window opening in a wall, includes a grill panel having a plurality of parallel, spaced, vertical bars fixed to a plurality of parallel, spaced, horizontal bars. The grille panel is of larger dimensions than the window opening such that the ends of the bars along at least one side project past the respective side of the window opening when the grille panel is mounted thereto. A plurality of fastening brackets mount the grille panel to the wall to cover the opening. Each bracket includes a loop section for slidably enclosing an end of a bar at the projecting side of the grille panel, and a fastening section for fastening the bracket to the wall after the loop section, while enclosing an end of a bar, has been slid along the respective bar to a location where the fastening section can be fastened to a mounting surface of the wall.