To the Dutch, water was more than the eternal enemy only.
Since the 80-years war of independence (1568-1648) against Spain, deliberately breaching the dikes was used as a painful but effective weapon against foreign invaders. It made the Spanish troops hate this cold, wet and with disease infested mess of a land.
In fact, this kind of defence was one of the reasons why the (low) Northern Netherlands gained freedom, and the (higher) southern part where the rebellion actually started (now Belgium and Northern France) remained occupied.
Over the centuries, an ever more ingenious system of dikes and locks was developed. To protect against the sea, but also against human invaders.
For a couple of clips with pictures of defence works over the centuries in the region: click here for video.
Lines of defence consisting of forts, bunkers, and trenches, covering with their fire a miles wide stretch of land that could be inundated on short notice. Flooded with deliberately shallow water, a bit less than a meter deep. Making the land difficult to cross for soldiers, vehicles and horses. Especially as all the deeper canals and ditches were now invisibly hidden under the water surface. While on the other hand the water had to be kept shallow enough to prevent the use of boats by the attacker.
These defences were used, and proved mainly an effective deterrent, until the Second World War. No match for paratroopers and planes, flying over it.
Nevertheless, until the end of the Cold War certain parts were secretly adapted to give the Russians some nasty surprises if they would dare to come. Which they never did, fortunately.
To protect Amsterdam and the heartland of Holland two elaborate defence lines were conceived.
One stretching from north to south, from the shores of the former Zuiderzee to the Rhine delta. The other a 135 km long circle of fortifications around Amsterdam (on the UNESCO World Heritage List).
Weesp and Muiden are the only towns in Holland that were part of both lines. So in this region, it is almost impossible NOT to see preparations for war somewhere around you. If you know where to look ... because a lot of the defences were very much of the stealth principle.
On the video page, links to a few clips on these subjects.
For more information on these defence lines, see www.stelling-amsterdam.nl and www.hollandsewaterlinie.nl.