Lighthouse

A lighthouse is a tower, building or other structure built to shine light from a system of lamps and lenses, serving as a beacon that guides maritime and inland waterway pilots. Lighthouses mark dangerous coastlines, shoals, reefs and rocks and also signal safe harbor entrances, though early lighthouses mainly marked the entrance to a port rather than warning of hazards. Before proper ports existed, sailors relied on hilltop fires, and raising these fires higher for greater visibility led to the lighthouse as a built form; the Pharos of Alexandria was the most famous ancient example before it collapsed following earthquakes between 956 and 1323. The number of working lighthouses has fallen sharply as GPS and other electronic navigation have reduced the need for them.