Fences and walls, doors, gates, turnstiles, traffic barriers, glazing (typically glass), and practically all construction materials are examples of man-made structural barriers. The main purpose of a barrier is to restrain movement of people or animals. Barriers can also be used to divide off different areas of land, for example a fence or wall around a garden. Barriers are used in many settings including prisons, military camps, schools, hospitals, factories, and public spaces like streets and parks. They are also used by animal control agencies when trying to contain dangerous animals such as lions or tigers within specific boundaries. Some barriers are more effective than others at containing threats within their bounds. For example, a fence is likely to be better at preventing people from entering an area than someone who is determined to get through it. Walls are built to prevent people from leaving an area, so they are usually more effective than fences at keeping threats in. The type of barrier used will determine how easy it is to pass. For example, a fence can be climbed over or cut through with simple tools, while a wall needs either a gunpowder charge or a lever-action rifle to breach. Threats that require physical force to overcome will not be contained by barriers; they can only restrict their movement.