Given my previous post about war and questioning the representation of it maybe it is a little perverse to set down to write a brief canter through the history of fortifications. However, defensive structures can, and have, prevented conflict for millennia. They have also be the focus of conflict, resistance, survival and defeat. Many castles are famous for their stories, others simply as landmarks. Primarily I will look at the situation in Britain, though I might wander off around the world later.
The function of most fortifications, be it a fort (purely military), castle (military but also a home to a politically important person) or a fortified city (largely civilian but often incorporating forts or castles) is to protect people or territory. Some, for example those built by Edward I, were also aggressive projections of power, built and used in a way analogous to the modern use of aircraft carriers.
The earliest defenses, back in the mists of time, were probably ditches and palisades of thorn bush or branches. This type of defense, better constructed and more scientifically considered had a very long pedigree. Arguably, in a slightly modified form, it returned in the modern era in the form of the trench systems of the First World War, substitute barbed wire for thorn bushes.
Iron Age Britain was covered in hill forts, many of which are still landmarks today. They vary in complexity but they are basically enormous variations on the same basic idea, one or more very deep ditches, often originally more than 6m deep, the spoil being used to increase the height on the inner side and create a platform that the defenders could use. The platform was topped with a wooden palisade of large stakes. In more sophisticated constructions the whole face of the inner side of the ditch might have been faced with logs that finished up as a wall to protect defenders on the inner side. The cover image for this post is a ‘reconstruction’ based on a photo I took at Old Sarum in Wiltshire. It just gives an idea of the scale of these earthworks and how formidable an obstacle they could be.
In some parts of the country, where timber was less available, dry stone walling was used instead to face the earth rampart and provide a covering wall. This reached its logical conclusion in the Scottish brochs – massive dry stone walled towers. Dry stone walls have a much earlier history in other parts of the world, famously at Jericho.
These very simple construction methods lasted in Europe well into the middle ages. The Saxons and the Vikings made use of wooden palisades and ditches to defend settlements, such as Birka and Hedeby. Famously the Normans built wooden motte and bailey castles during the conquest period, some of which remained in use into the 14th century.
Where the defender is not faced with large armies or sophisticated siege apparatus the wooden palisade atop a deep ditch, which may have additional obstacles such as sharpened stakes, is a perfectly viable means of defense and force multiplication. Being quick and cheap to build they also offered a ready solution for conquerors (the Roman marching camps were basic single ditch enclosures built in hours) and those seeking to achieve defense in depth – for example the system of Burghs developed by King Alfred and his successors against the Vikings.
The vulnerability of the wooden defenses were primarily against fire and against heavy projectile weapons which could destroy the palisades. They could not destroy the ditches themselves, which thus retained some defensive value if they were deep and steep enough. The scale of defenses is also limited in timber building. More sophisticated siege tactics and larger attacking units required more complex and robust defenses, which ushered in the widespread adoption of mortared stone walls…