Though the Dutch are nowadays quite peaceful, there have been a large number of wars in the past. A number of military objects remind us to this aspect of history. On this page a small guide is presented.
Several mediaeval castles bring you back to the 12th/13th century. The most famous is probably the castle Loevestein. You can find it near Gorinchem, which is also named Gorkum. From this nice town at the edge of the Alblasserwaard polder (worth a visit!) you cross the river Merwede with a small ferry, bringing you to Woudrichem, a well preserved stronghold. From Woudrichem you can go to the castle with another ferry. The castle is famous because the famous Dutch lawyer Hugo de Groot (Hugo Grotius) was kept there in prison. He managed to escape using a book case. You can visit the castle, which is worth the trouble.
Another still well preserved castle is Muiderslot, which is shown above at the image. The Muiderslot is about 12 km from Amsterdam and is open for visitors. You may like the castle Doornenburg, a bit south of Arnhem. It is not always open, but the Dutch television series "Floris" is recorded there. many Dutch still have good memories to this programme, the Dutch "Ivanhoe". Castle Doorwerth is the last one to mention here. It is possible to visit Doorwerth. According to the web site it's open every day except Mondays and public holidays.
Strongholds from the 80 year war
From 1568 till 1648 the Dutch were involved into a war with the troops op Philips II. This war was about religious freedom, but tax also played a role as far as I know. From the period a number of well preserved strongholds still can be visited.
In Groningen you can find Boertange, which is a kind of living museum. Boertange was surrounded by moors and swamps. It's rebuilt in its original state. Elburg is a completely different town. It's a harbour and fisherman's town at the coast of the former Zuyderzee. It has a rectangular city plan, designed for defence purposes. A cloister garden is one of the top attractions. Sometimes excursions to the defence works are organised by the tourist office.
(Image courtesy Michiel1972, Wikimedia)
In the province Brabant you may fancy visiting the town Heusden. The old town got its walls in the 16th Century and is beautifully restored recently. In North-Holland Naarden is worth vistiing and well known. Maybe it's the most famous stronghold in the country and a bit older than the others, dating mainly from the 14th century. See also Wikipedia. Naarden is attached to the educator and wrtier Comenius, who is buried in Naarden. The last stronghold I like to mention is Brielle in the province South-Holland.
Brielle still has the classic town lay-out as you can see on the Google Earth image. Brielle is very near Rotterdam.
The New Dutch Waterline
In the 16th and 17th century water already played an important role in the defence of the Dutch cities. The Nieuwe Hollandse Waterlinie (New Dutch Waterline) was a military line of defence of a much later date. 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, but never really worked. The German occupation showed it was useless against the German Air Force. Nowadays it's a Unensco monument and many of the fortresses still can be visited. To give you an overview, look in Google maps. Wikipedia provides some additional interesting information about this topic. A number of bicycle routes are provided as well.