Once the longest sea wall in the World

The original lighthouse at Poolbeg was built in 1768. This was redesigned into its present form in 1820 and was painted red to indicate ‘port side’ for ships entering Dublin Bay and the North Bull Lighthouse (on the other side of the bay) is painted green to indicate ‘starboard’. The Great South Wall extends nearly four miles out into Dublin Bay from Ringsend. It was the world’s longest sea wall at the time of its construction and still remains one of the longest in Europe. Navigation for sea vessels entering Dublin Bay and into the River Liffey has always been difficult and dangerous due to sandbanks and silting. In 1717 a decision was made to build a safe shipping lane with the help of a wall and so the first oak piles were driven in the boulder clay for what was to become the ‘South Bull Wall’. By 1795 the wall was completed with massive granite blocks brought from the quarries on Dalkey Hill. The base was 32 feet thick tapering to 28 feet at the top. Ordnance Survey Ireland also measured the low water mark of the spring tide on the 8th April 1837 and used this point as the standard height for all its maps until 1958.