A lighthouse is a tall structure, often located on coastlines or islands, designed to emit light and serve as a navigational aid for maritime pilots. The light helps ships identify dangerous coastlines, hazardous shoals, and safe entry points to harbors. Lighthouses often have distinctive patterns of light and color, making them easily recognizable from a distance. Lighthouses have been used for centuries, with some of the earliest examples dating back to ancient civilizations, such as the Pharos of Alexandria. They typically include a light source, a lens to focus the light, and sometimes a foghorn to alert vessels in poor visibility conditions.