But the fiercest struggle of all was the battle with the ocean. Holland, as a whole, lies lower than the sea-level; consequently, wherever the coast is not defended by downs it had to be protected by embankments. If these huge bulwarks of earth, wood, and granite were not standing like monuments to witness to the courage and perseverance of the Dutch, it would be impossible to believe that the hand of man, even in the course of many centuries, could have completed such an immense work. In Zealand alone the dykes extend over an area of four hundred kilometers. The western coast of the island of Walcheren is protected by a dyke, the cost of whose construction and preservation put out at interest would, it is calculated, have amounted to a sum great enough to have paid for the building of the dyke of solid copper. Round the town of Helder, at the northern extremity of Northern Holland, there is a dyke made of blocks of Norwegian granite which is ten kilometers long and stretches sixty meters into the sea. The province of Friesland, which is eighty-eight kilometers long, is protected by three rows of enormous palisades sustained by blocks of Norwegian and German granite. Amsterdam, all the towns on the coast of the Zuyder Zee, and all the islands which have been formed by fragments of the land that has disappeared, forming a sort of circle between Friesland and Northern Holland, are protected by dykes. From the mouths of the Ems to the mouths of the Scheldt, Holland is an impenetrable fort, in whose immense bastions the mills are the towers, the locks the gates, the islands the advanced forts; of which, like a real fortress, it shows to its enemy, the sea, only the tips of its steeples and the roofs of its buildings, as though in derision or in challenge.