A bollard is a short post used to create a protective or architectural perimeter. When installed primarily as a visual guide, they guide traffic and mark boundaries. As architectural elements they come in a wide variety of shapes and styles to accentuate or visually stand out in their settings. Bollards can also be constructed to physically block vehicle incursion, protecting people and property. These security posts may have decorative elements or be chosen to complement the landscape, but their primary consideration is resistance to impact forces. Bollards can be made from almost any material, depending on their needed function, but the most common materials are metal, stone, cement, or plastic. As vehicles become heavier and more highly powered than early carriages, installation and design of these posts has adapted in response. On one side of this equation are flexible bollards that can be hit without damage to car or post. On the other side are security bollards designed to protect buildings and pedestrian zones by slowing or stopping vehicles that hit them.
Vehicle attacks in public spaces have led to more interest in highly impact-resistant site protection. Government buildings sometimes install assault-resistant bollards designed to withstand multiple waves of vehicular bombardment.