About This Proposal
When people think of Japanese castles, they often imagine them with towering main keeps (tenshu).
However, most castles in the Sengoku period did not have main keeps. What actually formed the structure of these castles were stone walls, earthen ramparts, moats, and the surrounding terrain itself.
Another important point is that it was not only samurai who built fortified sites. Temples and local communities also constructed defensive or semi-fortified spaces as their bases.
Built by cutting into mountains, piling up earth, and making full use of the terrain, these structures reflected the very nature of society at the time.
Rather than viewing castles solely through the lens of the main keep (tenshu), this proposal interprets them as symbolic structures of their time, built by a diverse range of people.
From the upper left, clockwise: a Sengoku daimyo mountain castle, a fortified temple, a ninja residence, and a rural fortified settlement
Cultural Value
1. A Fragmented Sengoku Society
In the early Sengoku period, central authority in Japan weakened, and regional warlords, religious institutions, and local communities began to establish their own independent spheres of control. Castles were constructed primarily for defense and governance, spreading across the country as mountain fortresses and shaping a landscape of competing regional powers.
Rival castles and competing powers
This is the reality of the Sengoku period
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During the early Sengoku period, the traditional authority of shugo governors and the Ashikaga shogunate weakened, allowing regional powers to become increasingly autonomous.
For example, at Ichijōdani (present-day Fukui Prefecture), the Asakura clan built a castle town that functioned as a political and cultural center. In Omi Province (present-day Shiga Prefecture), the Azai clan constructed Odani Castle. These regional centers developed independently from Kyoto, forming alternative political, economic, and cultural hubs across Japan.
In parallel, religious institutions and autonomous communities also established fortified centers. Negoro-ji Temple (present-day Wakayama Prefecture) and Hyakusaiji Temple (present-day Shiga Prefecture) functioned as armed religious strongholds, while in Iga and Kōka (present-day Mie and Shiga Prefectures), local leagues (so) formed defensive communities. In Kaga Province (present-day Ishikawa Prefecture), peasant uprisings known as the Ikko-ikki established their own autonomous governance.
Most of these castles were mountain fortresses built in steep terrain, utilizing natural landscapes for defense. Defensive systems such as kuruwa, kirigishi, and Dorui formed the foundation of later castle architecture in Japan.
In the mid-16th century, the introduction of firearms further transformed warfare and castle design, bringing new technological and tactical changes to Sengoku society.
In this way, early Sengoku castles were not uniform structures, but rather regional fortifications built by diverse actors for different purposes, reflecting the fragmented social order of the time.
2. Unifiers and the Transformation of Castles
From the mid-Sengoku period, previously fragmented regional powers began to move toward unification. In the Kinai region, Miyoshi Nagayoshi first established wide-area control, followed by Oda Nobunaga, who further expanded territorial governance. Along with this shift, castles evolved from simple defensive fortifications into symbolic structures representing political authority and rule.
Castles enter the era of display
The age of the unifiers
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In the Kinai region during the mid-Sengoku period, Miyoshi Nagayoshi was among the first to achieve broad territorial control, establishing political power that rivaled the Ashikaga shogunate. This marked an important transitional phase leading toward national unification, during which castles began to shift from military strongholds to political centers.
Later, Oda Nobunaga expanded his influence from bases such as Komakiyama Castle and Gifu Castle. He gradually shifted castle construction from mountain fortresses to more accessible plains, redefining castles as both military bases and administrative centers of rule.
The most iconic example of this transformation is Azuchi Castle. Built with extensive stone foundations and a towering keep (tenshu), it was designed not only for defense but also to visually express authority. The surrounding castle town was also systematically developed, functioning as a political and economic center.
These innovations in castle architecture were influenced by the spread of firearms and contact with foreign cultures through Nanban trade. Sengoku Japan was undergoing profound transformation within a wider context of East Asian exchange.
This trend was later inherited by Toyotomi Hideyoshi. Castles were no longer merely facilities for warfare; they became central instruments of governance and symbols of authority over the realm.
3. Large-Scale Castles on the Path to Unification
In the final phase of the Sengoku period, Toyotomi Hideyoshi advanced the process of national unification. As a result, the role of castles expanded from regional strongholds into a state-level system of governance. Large-scale castles across the country came to symbolize both the end of the age of war and the emergence of a unified political order.
Castles become the center of the state
The final stage of the Sengoku period
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During the process of national unification, Toyotomi Hideyoshi established a network of large-scale castles across Japan. Osaka Castle served as its central hub, functioning as the political, military, and economic core of the emerging unified state.
Castles developed during this period were no longer limited to military purposes. They also functioned as administrative centers supporting wide-area governance. Koriyama Castle (present-day Nara Prefecture) represents an important early example of this transformation.
Ishigakiyama Castle (present-day Kanagawa Prefecture), built during the siege of Odawara, was a temporary yet massive fortress constructed in a very short time. Despite its impermanence, it became a decisive symbol of the end of the Sengoku conflicts.
In addition, Nagoya Castle (present-day Saga Prefecture, Nagoya Castle Site) was constructed as a base for the Imjin War, representing a mobilization system that extended beyond domestic unification to an East Asian scale. It reflects the maximum extent of castle development during the Sengoku period.
In this way, late Sengoku castles evolved into instruments of national governance, embodying Japan’s transition from a state of warfare to a unified political order.
Comparison with Existing World Heritage Sites
By comparing these sites with already inscribed World Heritage castles and fortifications, the value of the Sengoku castle ruins becomes even clearer. Click "click""tap" to view the comparisons.
Common point: A network of castles built as military and administrative bases that reflect historical transformation
Difference: Gwynedd represents conquest by royal authority, while Sengoku castles reflect a process from fragmentation to unification among multiple powers
Common point: Defensive structures built across regions by multiple powers using natural terrain
Difference: Rajasthan is centered on royal states, while Sengoku Japan includes a multi-layered society of warlords, temples, autonomous communities, and ninja groups
Common point: Fortified heritage from periods of conflict
Difference: Carcassonne is a single urban defensive system, while Sengoku castles represent a nationwide landscape of historical transformation
Common point: A competitive structure within a fragmented society
Difference: San Gimignano reflects rivalry among urban elites, while Sengoku castles reflect a militarized society including religious and autonomous forces
Next, a comparison with Japanese World Heritage sites. Click "click""tap" to view the comparison.
Common point: Represents the technological evolution of Sengoku-period castles, combining defense and authority
Difference: Himeji Castle is a completed single structure, while Sengoku castles represent the historical process of formation itself
Existing castle-related World Heritage sites, such as the Castles and Town Walls of King Edward in Gwynedd or Carcassonne, mainly focus on royal power or completed urban fortifications. In contrast, the "Sengoku Japanese Castle Ruins Group" represents a society in which warlords, temples, and autonomous communities coexisted, and the historical process that led to national unification. By visualizing social transformation through castles themselves, this proposal presents a value that is unique on a global scale.
Rationale for Selection
Here, we summarize why this proposal remains valid even when compared with other historical contexts. The reasons can be grouped into three key points. Click "click""tap" to view the details.
This proposal does not focus on individual battles or warlords of the Sengoku period, but rather on the process by which a fragmented society converged into unification. Therefore, castles associated with both unifying figures and opposing forces are included, presenting a clear historical turning point. Famous warlords such as Takeda Shingen and Uesugi Kenshin are not included for this reason.
The scope is not the entire Sengoku period, but rather its final phase, when fragmentation shifted toward national unification. Instead of the stable Edo period, this selection highlights a period of rapid structural transformation, clearly illustrating historical change itself. For this reason, castles associated with Tokugawa Ieyasu are not included.
By concentrating the scope in central and western Japan, it becomes possible to trace a continuous evolution from mountain fortresses to large-scale stone castles. This allows the transformation of the Sengoku period to be understood as a continuous process rather than isolated sites. Although famous castles are distributed across Japan, the selection is geographically focused to form a coherent narrative.
Through this integrated perspective of historical transition, dynamic change, and technological evolution, the nature of Sengoku Japan emerges more clearly as a unified historical landscape.
Components of the Property
Here we present the component parts that make up this proposed heritage site.
Please note that these are representative examples only, and not intended as a definitive or exhaustive selection.
Castles of a Fragmented Society
Castles of the Unifiers
Criteria
Let us organize the values discussed so far in terms of the UNESCO World Heritage criteria. This helps clarify the significance of the Sengoku castle sites.
Cultural Exchange
A hub of military and architectural exchange during a time of conflict
During Japan’s Sengoku period, new military technologies such as firearms, evolving battlefield tactics, and innovations in stone masonry and castle-town planning spread across the country. In addition, large-scale mobilization such as the base at Nagoya Castle reflects Japan’s connection with wider East Asian dynamics. These castle sites collectively illustrate an era deeply shaped by cultural and technological exchange.
Cultural Tradition / Civilization
A uniquely Japanese social structure of competing powers
In Sengoku Japan, not only warlords but also religious institutions, autonomous communities, peasant uprisings, and ninja-based networks exercised independent control and defense across the country. The castle sites associated with these groups represent a rare historical landscape of a highly pluralistic medieval society.
Architecture and Technology
The evolution of Japanese castle design from mountain forts to early modern fortresses
During the Sengoku period, Japanese castle architecture evolved dramatically from mountain strongholds to large-scale stone castles featuring advanced defensive and symbolic structures such as tenshu (keep towers). Innovations seen in castles like Azuchi, Osaka, and Ishigakiyama represent a major transition from medieval to early modern Japan.
In Closing
The Sengoku period was far from peaceful. It was an age marked by warfare, raids, and natural disasters—an era in which survival itself was a constant challenge.
In response, people built castles to protect their lives and sustain their communities. They cut into mountains, raised earthworks, and stacked stones, forming defensive bases across the landscape.
Over time, these efforts gave rise to large-scale castles such as Azuchi and Osaka, which came to symbolize the end of the age of war and the beginning of a new era.
In such uncertain times, what did people feel when they looked up at these castles?
Castles of the Sengoku period were not merely military structures. They embody the lives and struggles of the people who lived through this era.
The castles that remain today as stone walls and shaped landscapes are not just ruins, but the physical memory of those who endured the Sengoku period. They can be seen as monuments of an age of conflict—Monuments of the Sengoku era.
A “World Heritage Site” like this—why not?
