Cool discovery of Viking fort in Denmark leads to post giving TMI about the evolution of fort design

Because my readers in Denmark have been so aggressive lately and now are only a few dozen visits behind Sweden on the all-time visits list, I figured I would share this story, which I find fascinating:

Archaeologists in Denmark have discovered a distinctive ring-shaped Viking fortress which historians believe may have been used to launch an invasion of England.
The fortress found on the Danish island of Zealand, around 30 miles south of Copenhagen, is the fifth circular fortress to be unearthed, and the first in over 60 years.

Apparently these ring fortresses, built in around the late 900s, are scattered all over Denmark. They are

thought to date back to the late tenth century and the reign of Harald Bluetooth, the king who Christianised Denmark and Norway. However, some historians contend the fortresses were constructed by his son Sweyn Forkbeard, the first Danish King of England, as a military training camp or barracks from which to launch his invasions of England. Sweyn Forkbeard seized London in 1013 and was declared King of England on Christmas Day of that year.

Not much has been excavated of the newest discovery, but at least one of the other four ring fortresses previously discovered has been restored:

I don't know which one is pictured here, but the four previously discovered fortresses are located in Aggersborg and Fyrkat in northern Jutland, and Nonnebakken near Odense. Yeah, that doesn't mean much to me, either. Perhaps the Danes will check in with some enlightened commentary. I just dig historical shit like this and found it fascinating. Frankly, circular is a shitty design for a fort -- there are no mutually supporting positions on a circle. Once an enemy was up against the wall, there was no way to get rid of him except to hang over the top, exposing the defender to enemy fire. Compare that to this design, popular about 400 years later:

 This is a plan for what has been called Fort Raleigh, built in 1585 on Roanoke Island, North Carolina, by soldiers sent by Sir Walter Raleigh as an advance party for what became the Lost Colony. Google it -- I really don't feel up to explaining. Anyway, the fort was located by archaeologists and reconstructed about 80 years ago. Note the use of bastions to enable defenders to target attackers who had reached the wall. Defenders could aim along the wall to their left or right along the wall without exposing themselves to enemy fire. It looks kind of like this (couldn't find an aerial shot):

This method of using bastions continued for as long as forts were viable as a means of defense (rifled artillery rendered masonry forts obsolete about the time of the U.S. War Between the States). However, note that Fort McHenry, in Baltimore, which was the site of the battle that inspired Francis Scott Key to write the "Star Spangled Banner" during the War of 1812 between the United States and the United Kingdom, similarly used bastions, but these were placed at the corners rather than in the middle of the walls, as with Fort Raleigh:

as did the so-called Third System forts in the United States, built in the 1820s through the 1860s, such as Fort Pickens, built to defend Pensacola, Florida:

Obviously, one corner of the fort seems to have been blown off. It seems that way because it was. Sometime in the 1890s, I think, a gunpowder magazine in the now-missing bastion exploded, blowing away a pretty good chunk of the fort. Supposedly, the explosion was set off by the cigar of a soldier who was involved in a card game in the magazine. Don't know if that is true, but it makes a great story. When I lived in the area, we used to sneak into the fort at night and drink beer on the ramparts and look at the stars, among other things. There is a strong possibility that some of the folks with whom I used to drink beer on the ramparts might have picked up a stray brick or two left over from the magazine explosion. Back then, they were all over the place. I went back a couple years ago, and didn't see any bricks around. The Park Service must have cleaned up, finally.

Anyway, the point of this digression is that circular forts suck. Sweyn Forkbeard might have conquered England, but his guys only held it until 1066, when William of Normandy came over and kicked their circular-fort-building asses. William might have known fuck-all about bastions, but he obviously was not intimidated by circular forts. Nonetheless, I find 1,000-year-old forts, circular or otherwise, to be pretty fascinating. Sorry if you didn't. And yes, I chose the non-Viking forts discussed here because I have spent a lot of time prowling the grounds of and studying all three of those forts. Sue me for being biased.