For centuries, the water lapped against the mound on which the St. Willibrordus Church of Holwerd is built during high tide. The mound, where the church was built shortly after the Christianization of the Frisians by missionaries Boniface, Liudger, and Willibrord, was outside the dikes until 1580. The wooden church was replaced in the 12th century by a tuff stone building. The tower served as a beacon for shipping. The Wadden Sea was treacherous, but thanks to beacons like church towers, sailors could guide their ships to safe harbor.