The Ōnin War (1467–1477) shattered Ashikaga authority and devastated Kyōto, helping trigger a century of endemic warfare. The prolonged conflict increased demand for defensible local strongpoints and accelerated the evolution from temporary fieldworks toward more permanent castle complexes.
Ishiyama Hongan-ji was established as a fortified Buddhist temple complex at Osaka (traditionally dated to 1496). Its location and defenses made it a major stronghold and a central case study for late Sengoku siege warfare against entrenched religious leagues.
By the 1530s, Japanese military architecture began incorporating significant stone structures, marking an important shift toward more durable fortifications. This transition laid groundwork for the large stone bases and walls that became defining features of early-modern castles.
Oda Nobunaga’s forces began a long campaign against Ishiyama Hongan-ji (commonly dated 1570–1580). The struggle highlighted the difficulty of reducing well-supplied fortresses—especially coastal ones—and drove the construction of surrounding forts and blockading works.
During the 1575 fighting around Nagashino Castle, Oda Nobunaga’s forces employed wooden palisades to protect matchlock gunners. The episode is widely cited for showing how rapidly firearms affected field fortifications and defensive preparations in siege relief operations.
Azuchi Castle—ordered by Oda Nobunaga and completed in 1579—became a landmark in castle design, pairing formidable stonework with a prominent tenshu (main keep). Its scale and symbolism influenced subsequent monumental castle-building during unification.
In August 1580, Abbot Kennyo (Kōsa) surrendered, ending the protracted siege. The fall of this fortress-temple marked a major turning point in suppressing militant Ikkō-ikki networks and cleared the way for Toyotomi redevelopment of the Osaka site.
Toyotomi Hideyoshi began building Osaka Castle in 1583 on the former Ishiyama Hongan-ji site, modeling key aspects on Azuchi while aiming to surpass it. The project exemplified late Sengoku “megacastles,” combining huge stone bases, moats, and political theater.
By 1585, Osaka Castle’s inner donjon (central tower complex) was completed, while Hideyoshi continued to expand the overall defenses afterward. This staged construction reflects how major castles were built and upgraded in phases as strategic needs evolved.
Toyotomi Hideyoshi’s 1590 siege of Odawara (May–August) forced the Later Hōjō clan’s surrender, demonstrating unification-era siege logistics at massive scale. The campaign helped consolidate Toyotomi power and reduced the number of autonomous regional fortress networks.
Toyotomi Hideyoshi constructed Fushimi Castle (1592–1594), a major fortified residence near Kyōto that also anchored a large castle town. Its combination of defensive form and elite residential function illustrates how castles became administrative and ceremonial centers, not only battlefield posts.
Construction of Osaka Castle is commonly dated as completed in 1597 (with continued enhancements earlier and intermittent damage from events such as the 1596 earthquake). The finished complex became the premier Toyotomi stronghold and later the focal point of Tokugawa siege operations.
Ikeda Terumasa undertook a major overhaul of Himeji Castle between 1601 and 1609, producing much of the complex seen today. The work showcases early Edo advances in stone retaining walls, layered baileys, gates, and routes designed to slow attackers under missile and firearm fire.
The Siege of Osaka opened with the Winter Campaign beginning on November 8, 1614, when Tokugawa Ieyasu moved against the Toyotomi at Osaka Castle. The operations underscored the strategic value of deep moats, massive stonework, and outer defensive lines in resisting superior numbers.
Fighting resumed in the Summer Campaign (May–June 1615) and culminated in Tokugawa victory and the destruction of the Toyotomi. The outcome marked the end of the Sengoku-era cycle of grand sieges and removed the last major rival fortress to Tokugawa rule.
In 1615, the Tokugawa shogunate issued the Ikkoku ichijō (one castle per province) policy, ordering the reduction of castles across domains. This measure institutionalized post-Sengoku demilitarization by limiting new construction and forcing dismantlement of many secondary forts.
Castle construction and siege warfare in Sengoku and early Edo Japan (1467–1615)
