On a squally day in Dublin bay, gardaí park up on the Great South Wall, placing their car and authority in front of the walkers who come to the wall to watch waves dominate it.  At high tide and in high winds, the wall, which culminates in the Poolbeg Lighthouse,  becomes dangerous as parts of it are submerged and impassable.  Beloved by Dubliners as the improbable pathway from the middle of the bay to the chimney stack gateposts of the city, it’s been a capital feature for close to three centuries. Built out of necessity for sailors and seafarers, who…