The Nieuwe Hollandse Waterlinie (New Dutch Waterline) was a military line of defence. The line was established as a protective ring approximately 85 km long and 3–5 km wide around the Dutch cities of Muiden, Utrecht, Vreeswijk and Gorinchem.
It was the main Dutch defence line from 1815 till 1940.  The Nieuwe Hollandse Waterlinie’s primary element of defence was water. Land was intentionally flooded (inundated) during times of war to obstruct the enemy. A layer of water of only 40 cm deep, was enough to make the land difficult to pass for soldiers, vehicles and horses. At the same time, it was not deep enough to navigate by ship.
By 1870, the waterline could be inundated within three weeks thanks to an ingenious system of sluices, dikes and flood canals.
 
Weak points along the natural defence line were strengthened with forts, bunkers and group shelters. In addition, the line included five fortified cities: Muiden, Weesp, Naarden, Gorinchem and Woudrichem.
 
Although the Nieuwe Hollandse Waterlinie never had a chance to prove its worth as a line of defence, it has been brought into a state of emergency three times. First in 1870, when the Franco–Prussian War threatened to turn into a European war. Second, during the First World War, and finally in 1939 when the Second World War broke out.
Many places and buildings which belonged to the Waterlinie still are visible today, such as the forts and other defence works. Today, every fort has a different purpose, for example, a camping site or a wine cellar.
The book "Living Forts' shows the new functions of the buildings of the Nieuwe Hollandse Waterlinie.
 

Echoes of the Slave Trade in Ghana
 
The coast of Ghana was once lined with more than 40 forts, where European colonials once carried out an inhuman trade in living cargo, shipping untold numbers of Africans against their will to the New World to work as slaves.
And for almost 200 years, from 1637 until 1814, when the Netherlands abolished its slave trade, the Dutch West Indies Company was involved at the heart of this sordid traffic. I travelled to Ghana and found lingering memories in the evidence of this dark past, and also met a proud people willing to talk about their ancestors who passed through the ‘door of no return’.