81 watchtowers were built between 1804 to 1817 along the Irish coast as an integrated defence system to deter an invasion from Napoleon. The watchtowers were located going clock wise from Dublin right up to Malin Head.
Each watchtower was built within view of the next watchtower and flags would be raised to send a signal onto the next tower. A signal could travel from Malin Head in County Donegal right around the coast line to Dublin and then back again.
Not all of the watchtowers survived the test of time but the majority of them can still be spotted around the Irish coast.