Why would people build a wall out of rocks on a seashore?

People build walls out of rocks on a seashore primarily for coastal protection against erosion and storm surges. These structures, known as seawalls or riprap, help stabilize the shoreline, preventing land loss and damage to infrastructure. Additionally, they can serve as habitats for marine life and enhance recreational areas for beachgoers. Overall, they are a practical solution to mitigate the effects of natural forces on coastal environments.