December 14th was the anniversary of the St. Lucia flood of 1287, which resulted in the deaths of at least 50,000 people in the Netherlands. It's one of the largest floods in recorded history, and it was the result of a storm tide: an extreme low-pressure system that coincides with the high tide.
Much of the damage caused by Hurricane Sandy in 2012 was the result of a similar storm tide. The Zuiderzee sea wall built to hold back the water couldn't stand against such forces, and it collapsed. The North Sea rushed in, killing thousands and reclaiming huge amounts of land in the northern part of the Netherlands. The Zuiderzee — which means "southern sea" — actually owes its origin to this storm. It had originally been a series of shallow inland lakes and marshes, but storms and tides gradually ate away at the edges of the separate lakes, and when the North Sea encroached on the land as a result of the storm, the lake became a bay.
Flooding has always been a matter of great concern to people in the Netherlands. Two-thirds of its area is considered to be at risk, and much of it is an alluvial plain: land formed by the buildup of silt deposited by floods. The rich soil attracted early farmers, who built artificial hills called terpen to live on. They also built low embankments to keep out the water, and by 1250, dike construction was a major industry. The church was the biggest and richest landowner, and the monasteries provided the most readily available workforce, so they took the lead in dike construction, and eventually all the dikes were connected into a continuous seawall.
The massive St. Lucia storm of 1287 also affected the coast of England. The effects weren't as immediately dramatic, but the storm dumped silt into the harbors of several key port cities and made it impossible for ships to enter. The English coastline was redrawn, and the cities never regained their status as vital trading ports.
[this is from the writer's almanac entry for 14 Dec 2013]