Age of conflict

From the 15th century onwards, Japan entered an unstable era as civil wars weakened the power of the central government. Local powers began to seek ways to maintain their influence through self-governance, and as a result, the country entered an era of civil war. This was the beginning of the Sengoku period.

The most representative local powers were the Sengoku daimyo. They built castles on mountaintops and steep terrain, and ruled their territories while preparing for invasions from foreign enemies.

In addition to the Sengoku daimyo, temple and shrine forces also had their own military power. Armed monks called 'Sōhei' were organized, and they boasted strength that rivaled that of samurai. Temples themselves were fortified, and they faced off against other regional forces like castles.

In areas beyond the influence of Sengoku daimyo or their own companies, republican-like governance was practiced, with the people making decisions through consensus. These gatherings of the people were called ikki. Typical examples include Iga and Koga, famous for their ninjas, and Kaga, known as the "country of peasants." Even in these spheres of influence, castles were built to counter external forces. In Iga and Koga, each house had its own wall and earthworks. In Kaga, the people came together to build large castles. What united the people was Buddhism, such as the Ikko sect. United by Buddhism and using castles for defense, the ikki became a force that even Sengoku daimyo could no longer ignore.

As mentioned above, Japan's Sengoku period was a unique time in the world, in that people of all social classes built castles, governed themselves while defending themselves against invasions from foreign enemies.

Age of the Unifiers

It was the rulers of Japan who brought an end to this chaotic era.

The first ruler of Japan is said to be Miyoshi Nagayoshi. After gaining power in the central government, he built large castles to stabilize the surrounding Kinki region, and used them as bases for running the government. Furthermore, this large-scale castle was the first in the country to make extensive use of stone walls, demonstrating his power. Miyoshi Nagayoshi's castle had a great influence on castle architecture thereafter.

After the Miyoshi government was short-lived, the next ruler of Japan was Oda Nobunaga. While the Miyoshi government was responsible for pacifying areas under the influence of the central government, Oda Nobunaga pacified a wide area, including his base in northern Aichi Prefecture, as well as the Chubu and Kinki regions. In the process, Nobunaga gradually weakened or destroyed the resistance forces of the Sengoku daimyo, temple and shrine forces, and popular uprisings. This marked a shift in direction from an era of local power to one of centralization. As a symbol of this, large castle towers were built for the first time in castles, with the aim of demonstrating power.

Toyotomi Hideyoshi succeeded Oda Nobunaga. He destroyed or subjugated the remaining resistance, finally bringing the Sengoku period to an end. Under Toyotomi's government, castles, which had been built on mountaintops for defensive purposes, were rebuilt on flat ground and came to function as symbols of power.

To summarize the above, we can see the change in the role of castles from a chaotic era to the centralization of power by the rulers of Japan.

Castles have been built in Japan since ancient times, but the period when they were most developed was the Sengoku period.

In ancient Japan, castles were built on a national scale and made the most of the natural terrain. However, as the power of the state declined in the Middle Ages, local lords began to build their own castles. Then, during the Sengoku period at the end of the Middle Ages, the soil was removed from the mountains and complex structures such as Kuruwa [Enclosure], Kirigishi [Artificial cliff], Dorui [Earthwork], and Karabori [Dry moat] were arranged, dramatically improving defensive capabilities. Other technological innovations included the use of stone walls, which in ancient times were only used to reinforce earthen ramparts, as castle walls themselves.

Then, during the era of the unifiers of Japan, castle technology also underwent major changes.

Miyoshi Nagayoshi changed the role of castles from the traditional defensive mountain castles to mountain castles that combined defense and served as government offices. At this time, he built large-scale castles with extensive stone walls and large-scale Kuruwa [Enclosure] to demonstrate his power.

Castle architecture using stone walls underwent a major revolution under Oda Nobunaga. Oda Nobunaga made extensive use of stone walls, and was the first to build large-scale structures on top of stone walls, which traditional earthen castles could not withstand. This was the castle tower. Azuchi Castle in particular is known for being the first castle in history to have a large-scale castle tower built. The castle tower functioned as a symbol of authority, and had a huge influence on castle architecture thereafter. It can be seen that Oda Nobunaga marked a turning point in castle architecture.

Then, Toyotomi Hideyoshi transformed the castle into a "stone wall castle" built entirely out of stone. Castles that were once built for defensive purposes were transformed by Toyotomi Hideyoshi into castles to be "shown off," and as a result, sturdy stone wall castles began to be built.

To summarize the above, we can see that castle-building techniques changed dramatically during the Sengoku period, from "earthen castles" to "castles made entirely of stone walls." In the process, large-scale buildings such as castle towers began to be built, and it was a time of rapid advancement in construction technology, even by global standards.

The Sengoku period in Japan corresponds to the Age of Discovery in Europe. Missionaries and other Europeans came to Japan and recorded their experiences and events in Japan in diaries. Many castles from the Sengoku period are mentioned in these diaries. These diaries are known as important sources of information, as they contain descriptions of castles, their construction techniques, and even their prosperity and decline.

The places where the missionaries received hospitality were the castles of the unifiers of Japan, which also functioned as places of exchange between Europe and Japan.

Castles from the Sengoku period, which served as places of exchange between Japanese and Europeans, are also a memory heritage that connects Europe and Japan.

The above information can be summarized in the following figure:

The castles of the Warring States period, which underwent unique technological innovation and became a place of global exchange, are truly a cultural asset that we can be proud of around the world!

There are seventeen in total.

Ichijodani Asakura family site Museum
Japan Heritage/ Shinobi-no-Sato Iga and Koka
Japan Heritage/ A Ruthless Warlord's Spirit of Hospitality
Shiga Prefectural Azuchi Castle Archaeological Museum
Osaka Castle Museum
Saga Prefectural Nagoya Castle Museum