This illustration, from History of Europe: Ancient and Medieval, shows the magnificence of Château de Coucy, a French castle that was built in the early 1200s and blown to smithereens by the German army about 700 years later during World War I.
The huge round tower in the forefront is the keep/donjon, which was one of the largest such fortifications in the world. It measured between 100 and 115 feet wide and between 180 and 210 feet high. According to History of Europe: Ancient and Medieval, the walls were 34 feet thick at the base.
This is all that remains of the grand castle today...
According to Wikipedia, one of Château de Coucy's lords, Enguerrand VII de Coucy (1340–1397), is the primary subject of Barbara Tuchman's award-winning narrative of the fourteenth century, A Distant Mirror, which was published in 1978.
For a wealth of information about and images of Château de Coucy, see the English-language version of this website by Pierre-Emmanuel Sautereau, which focuses on pre-1917 postcards and photographs.
(While I am very happy that Sautereau provided an English-language version of his history website, I think there were some translation problems with this section:
"This site aims to help you discover Coucy-le-Chateau, through postcards and old photos, collected by several collectors. They agreed to share their treasure, I thank them all very much. These documents are obviously for personal research, not for breeding purposes."And, just to be clear, that goes for all of the ephemera on Papergreat, too. None of it should ever be used for breeding purposes.)