Bleachers are tiered rows of benches or seats, typically found in sports venues, schools, and outdoor event spaces, designed to accommodate spectators. They are constructed to provide an elevated view of the event, ensuring that even those seated at the back can see over those in front. 
Bleachers can be made from various materials, including wood, aluminum, or steel, and are often designed to be either permanent or portable. Permanent bleachers are fixed structures, usually made of more durable materials like concrete or metal, and are often found in larger stadiums. Portable bleachers, on the other hand, are designed to be moved and reconfigured as needed, making them ideal for schools or smaller venues that host different types of events.
The basic structure of bleachers involves a series of horizontal platforms, or "risers," which are supported by vertical posts or frames. These risers are arranged in ascending order, creating a stepped effect. Each riser typically supports a bench or individual seats, allowing spectators to sit comfortably while maintaining a clear line of sight to the event.
Bleachers work by maximizing space and visibility. The tiered design allows a large number of people to occupy a relatively small footprint while ensuring that each person has an unobstructed view. This is achieved by the elevation of each successive row, which is higher than the one in front of it. Additionally, the open design of bleachers facilitates easy movement and access, allowing spectators to enter and exit quickly.
In summary, bleachers are an efficient seating solution for large crowds, providing elevated views and maximizing space through their tiered design.