The South Stack Lighthouse has warned passing ships of the treacherous rock below since its completion in 1809. The 91-foot (28 m)-tall lighthouse on South Stack was designed by Daniel Alexander and the main light is visible to passing vessels for 24 nmi (44 km; 28 mi), and was designed to allow safe passage for ships on the treacherous Dublin–Holyhead–Liverpool sea route. It provides the first beacon along the northern coast of Anglesey for east-bound ships.