Linn Duachaill (Irish pronunciation: [ˌl̠ʲiːn̠ʲ ˈd̪ˠuəxəl̠ʲ]; "Duachall's pool") is the name of a Viking longphort near the village of Annagassan, County Louth, Ireland. The settlement was built in 841 CE, the same time as the settlement of Dubh Linn, or Dublin. In contrast to Dublin, the settlement was abandoned. It has been argued that possibly because of changing tidal patterns, it lacked continuous access to the sea. The tides would have made access to the water difficult for a number of hours per day. History.
https://en.wikipedia.org/wiki/Linn_Duachaill