Abstract: A door-like closure for passageways in high-risk high-security installations includes a multilayer protective plate which has a rather high resistance to mechanical, thermal and chemical damaging influences, but which can be rather easily damaged by the action of explosives. To reinforce the protective plate, a reinforcing grid is juxtaposed therewith at the major surface thereof which faces the interior of the installation so that, when an attempt is made to destroy the protective plate by explosives, the reinforcing grid not only will increase the resistance of the protective plate to damage but also will permit the explosive shockwave and the possible debris of the protective plate propelled thereby to penetrate through the apertures of the grid without causing any considerable damage to the grid. The apertures of the grid have such dimensions that an intruder will not be able to reach through the aperture into the interior of the installation to, for instance, manipulate the lock of the closure.