The walled city of Chieshi lies at the heart of my Fumetsu Cycle of novels: Preserving Eternity (November 2015), Declining Eternity (due mid 2016), and Restoring Eternity (due late 2016). Although the idea for the city was inspired by the West Asian city of Troy the architecture of the city's defences is based on Kumamoto Castle in south western Japan. So it was with sadness that I noted that the major earthquake that struck that country on 14th April 2016 hit the Kumamoto region on Kyushu Island. The castle has endured some damage, but the major casualties are at the epicentre of the earthquake in Mashiki 16 miles to the east. Thankfully it appears that the death toll is low, partly due to Japanese building regulations being so strict in the wake of earthquakes in previous decades.
Building with a view to earthquakes is not a modern phenomenon in Japan. It is a country with earthquakes featuring as part and parcel of their history and they influenced the very different look of a Japanese castle to what someone familiar with medieval Europe would envisage. As in Europe castles played an important role in a more volatile pre-modern history. Lower populations and great inequalities of wealth meant that in both Europe and Japan wealthy leaders could forge military victories with relatively small numbers of warriors. As a consequence it was important to have a place of refuge to protect the general population and castles provided that function, but in different ways in Europe and Japan. A large reason for that difference is that Japanese castles had to be built with a view to earthquake damage.
The stereotypical image of a European castle is of tall and straight stone walls that were designed to resist the siege attacks of enemies. It is an image dear to my heart as a former resident of North Wales, which has a ring of stone castles built by the English, which are still standing and are now major tourist attractions in very Welsh towns. Someone used to that image of a castle will be surprised to see the typical design of a Japanese castle. It was only in the tail-end of the castle building era around the 16th century by European reckoning that stone was used in castle building in Japan. This is because of the wider view of safe construction in Japan that favoured light building materials. Those lighter materials were not so much that they were less likely to kill its inhabitants during an earthquake, but that they could more readily be designed to tolerate a certain amount of earth tremors. The earliest Japanese castles were little more than large houses on the top of a hill and a series of castles might be built on neighbouring hills. So there was little difference between the construction techniques for a house than for a castle. That meant that part of the defence for the non-warriors was the hill that the attacking army had to climb, but the main defence was the castle's warriors as castles were more for protection of non-combatants and the battle took place in the plain outside the castle.
As power concentrated more in the hands of the daimyo (regional overlord) castles became more like the European version, except that they were made of wood. The image of a fort of the early United States Cavalry would be a better representation of what they looked like than the medieval English castles of North Wales. Those wooden walls included platforms on which warriors could stand, but that was more to allow for lookouts than to repel invaders. Even as Japanese castles moved to a size of their European equivalents the military culture remained one of the defenders running or riding out to engage the enemy on the battlefield. These wooden castles were often built on hills reflecting the earliest history of castle building, although sometimes it was an artificially constructed embankment, rather than using the natural version.
The stone period of Japanese castle construction is represented best by Kumamoto Castle and to the European eye their most surprising feature is that it is not an entirely stone structure. The battlements are still wooden, but now very large and looking more like the large houses that were the earliest castles. Another surprise to the European is that the walls are gently sloped, which seems foolish as it would allow the enemy to scale the wall more easily. Yet think back to the history of castle architecture. They begin as houses on top of hills, then become larger wooden structures on top of often artificial embankments. So the stone wall of a Japanese castle is better thought of as a stone covered embankment, which is in fact what it is.
The sloped wall may make for poorer siege defence, especially as the wooden battlements were vulnerable to fire, but a straight wall is more susceptible to earthquake damage. That is evident in the photographs of the damage to Kumamoto Castle in the 2016 earthquake in this Guardian article. Part of the castle's stone wall collapsed in the earthquake to reveal that the stone was covering a mound of earth. Consequently it is easier to rebuild a castle wall so long as a castle is not too close to the epicentre of the earthquake. The high straight walls of a European castle could not be constructed with earthen works in the same way, so an earthquake would leave a major gap in the defences until the wall was reconstructed. The photograph reveals something else about those sloped walls of Kumamoto Castle. If you look at the non-collapsed part of the wall you will see that there is no mortar between the stones, which is part of the earthquake defence. Mortar adds rigidity to a wall and in an earthquake zone rigidity is a problem. The lack of mortar and the earth below the stones allows slight amounts of movements, which enables the wall to withstand most earth tremors.
The constant threat of earthquakes explains those sloping walls in Japanese castles, but it does not alter the fact that they were easy to climb. What Europeans can forget, though, is that they are easy to climb in both directions. One of the limitations of European castle siege warfare was that is gave most of the initiative to the besieger. The weakest point of a castle wall is its gate and so gates were limited in number. Yet that meant limiting the exit points for the defenders to take the battle to their enemy and making it easier for the besieging forces to guard those exit points. In a Japanese castle the cavalry are still limited to the gates, but the foot soldiers can climb down the walls that the attackers can easily climb up. That enables defenders to live up to the feudal Japanese tradition of taking the battle onto the plain. Do not think of this battle in terms of modern movie depictions and therefore assume that any besieging force would surround every square inch of the castle walls. The numbers of combatants in medieval warfare was often quite low. This was especially the case in Japan, which faced little threat from foreign invaders and spent most of its military history fighting other Japanese. With a lower number of combatants the defending foot soldiers could climb down their own castle walls to outflank the attacking forces. Feudal Japan had different castles to Europeans in part because they had a different attitude to the role of a castle in warfare. Castle design was also connected to being in one of the most earthquake volatile regions on Earth.