Skuldelev Ships: Five Viking Ocean Serpents Sacrificed 

The first interesting thing about the burial was that five ships were sunken in the  same spot. The second awesome thing was that they were sunken because the Vikings wanted that.

The year was around 1000 A.D. The Vikings filled the 5 ships with stones and let them sink. They did so because they wanted to block the ship channel which provided access to the town. In this way could the town inhabitants protect themselves and their land from the enemies. 

At first, three ships were brought to the narrowest point. After twenty years, other two ships were brought out and sunken. Then the defensive added more ships, making it an effective defense system.

Around the 1960s, what thought to rest in the ocean forever finally revealed themselves. The site drained, turning into a cofferdam and there came the excavation.