なぜ奈良盆地南部で『大和』は始まったのかWhy Yamato Began in Southern Nara Basin

The most crucial symbols for the legitimacy of the emperor are the Sanshu-no-Jingi (三種の神器, Three Imperial Regalia). However, historical accounts from descendants of ancient clans suggest these regalia might not have originally consisted of the currently recognized trio—the Yata-no-Kagami (八咫鏡), the Kusanagi-no-Tsurugi (草薙剣), and the Yasakani-no-Magatama (八尺瓊勾玉). Previously, I mentioned how the Imibe clan (忌部氏), an ancient family responsible for significant imperial rites, gradually lost their power within the imperial court due to the rise of the Fujiwara clan, whose roots trace back to the Nakatomi clan (中臣氏), also tasked with performing sacred rites, leading eventually to their disappearance from history.

In this context, Imibe no Hironari (斎部広成), a descendant of the Imibe clan, compiled and presented ancient traditions related to his lineage at the behest of Emperor Heizei (平城天皇, reigned 806–809), who sought to check the Fujiwara clan’s growing influence during the early Heian period—a time effectively dominated by the Fujiwara. Over 80 years old at the time, Hironari submitted this compilation titled the Kogo Shui (古語拾遺, 807). According to this text, imperial legitimacy originally relied on only two regalia, excluding the Yasakani-no-Magatama, which is described as having possibly been later offered as evidence of submission from another tribe or clan.

The account I share today is based on writings left by descendants of a clan even older than the Imibe. This document claims that prior to the establishment of the Sanshu-no-Jingi, a distinctly different entity held power in Yamato (大和), asserting legitimacy through entirely different sacred regalia. The clan responsible for these writings was the Mononobe clan (物部氏), one of the most historically significant families of ancient Japan. To grasp the role played by the Mononobe, however, we must adopt a broader perspective that has seldom been considered before.

The Mononobe clan traces its origins to Umashimaji (宇摩志麻治命), a prominent figure in Japanese mythology. The clan held supreme religious authority within Shinto and wielded military power, particularly before Buddhism was introduced to Japan. Historical upheaval began around 538–552, when King Seong of Baekje (modern southwestern Korea) offered Buddhist statues, scriptures, and monks, originating from China, to the imperial court located in Yamato (now southern Nara Prefecture). Before these tumultuous events, the Mononobe had overwhelmingly dominated the region.

However, the introduction of Buddhism drastically shifted the power dynamics. The Mononobe rapidly declined as the Soga clan (蘇我氏), a newly rising family based in the Asuka region—populated significantly by immigrants from China and the Korean Peninsula—quickly gained power by unifying the migrant communities, leading to the eventual disappearance of the Mononobe from history. Although the theory of the Soga clan having foreign origins has recently gained traction in Japan, I believe the southern Yamato area (the southern Nara Basin region) during this period was a complex multicultural zone, home not only to immigrants from China and Korea but also to numerous internal migrants from various parts of Japan such as western regions and the Tokai area, all competing fiercely for influence. These complicated origins place this period squarely within Japan’s Kofun period (古墳時代).

Thus, Yamato at this time functioned as a federation of various tribes, but it is essential to understand that its origins did not span the entire modern Nara Basin but rather a considerably limited portion. A major reason for this was the presence of optimal environmental conditions for wet-rice agriculture specifically in the southern basin region of Yamato. Additionally, the Mononobe clan considered their lineage to originate from the deity Nigihayahi (饒速日命), asserting that Nigihayahi represented legitimate divinity prior to the arrival and ascension of Emperor Jimmu (神武天皇), known initially as Kamuyamato-Iwarehiko (神倭伊波礼比古命), who established his rule in Kashihara, southern Yamato.

Nigihayahi appears briefly in both the Kojiki and Nihon Shoki; the Kojiki vaguely refers to him as the ancestral deity of the Mononobe without providing details, while the Nihon Shoki offers somewhat more description, though still incomplete. After losing political power at the imperial court, the remnants of the Mononobe clan attempted to reassert their legitimacy by suddenly presenting a written compilation of their ancient traditions. This text is the Sendai Kuji Hongi (先代旧事本紀), believed to have been composed around the first half of the 10th century, though its authorship remains unknown. For centuries, its authenticity has been debated extensively, but recently it has gradually gained academic recognition as genuine, leading to slow but progressing research—although it still remains far behind the scholarship dedicated to the Kojiki and Nihon Shoki.

According to the Sendai Kuji Hongi, Nigihayahi arrived in Kawachi Province (around modern-day Ikoma Mountains near Osaka) bearing the Tokusa-no-Kandakara (十種神宝), a set of ten sacred regalia, accompanied by numerous retainers. He subsequently migrated to and governed Yamato. This account is quite complex, so I plan to delve deeper into it gradually in future articles. However, at this point, it is important to examine why exactly the imperial court was established specifically in the southern region of Yamato. Understanding this issue connects directly to Nigihayahi’s actions and provides a fundamental entry point for interpreting the mythology outlined in the Kojiki and Nihon Shoki.

Although rarely discussed, why exactly was the Yamato Court (大和朝廷) established in the southern part of the Nara Basin? Today, the northern part (near modern-day Nara City), which became historically prominent after the establishment of Heijo-kyo (平城京) in 710, is far more famous. Having extensively explored the entire Nara Basin myself, I have long pondered this question. Notably, the central area of the Nara Basin has historically been almost a void, rarely serving as a political hub except in isolated instances. From another perspective, the ancient groups inhabiting Yamato gradually shifted their political centers—from the southern basin near the mountainous border with Osaka (particularly the northern and southern foothills), eventually moving northward toward the region near present-day Nara City.

The crucial question here is: Why did ancient peoples initially concentrate in the southern part of the Nara Basin? Given its vastness, settlement could just as easily have begun in the central or northern parts. However, ancient Yamato’s history clearly starts in the south. The key to solving this mystery lies in a lake, which is unimaginable today. Hundreds of thousands of years ago, the current Nara Basin, Osaka Plain, and Kyoto Basin were part of a vast sea and lake system. Over time, as sea levels gradually fell, these basins and plains were formed.

A remnant of this ancient lake survived into historical times, covering much of the central to northern part of the Nara Basin. This lake undoubtedly existed during the Jomon period, and references to a lake even appear in poems from the Manyoshu (万葉集, ca. 759), suggesting it persisted, albeit shrinking, until quite recent historical times.

This lake is known as Lake Yamato (大和湖). Yet, until recently, it has largely remained unexplored academically. Masami Senda (千田正美), a pioneering researcher who spent his life conducting empirical fieldwork in the Nara Basin, was the first to comprehensively illuminate this lake. He summarized his groundbreaking findings in 1978, introducing a previously unconsidered perspective. However, since he was not a university professor, his work was academically ignored and sidelined—a common occurrence in Japan.

Consequently, this crucial insight remained largely unexplored for nearly fifty years. However, recently, parts of Senda’s theories have gained recognition at Kansai University, attracting renewed attention. According to Senda, the expansive Lake Yamato originally formed by tectonic subsidence drained gradually toward the Osaka Plain, lowering its water level to around 50 meters elevation by approximately 2,500 years ago. This fault is located near “Kame-no-se” (亀の瀬), an area along the Yamato River between the Ikoma and Kongo mountain ranges at the junction of the Osaka Plain and Nara Basin, historically notorious for frequent landslides.

Significant landslides in this region from the Jomon to Yayoi periods caused Lake Yamato’s waters to flow out into the Osaka Plain, steadily lowering the water level and creating extensive wetlands around its perimeter. My own repeated investigations into settlement patterns during the Jomon, Yayoi, and Kofun periods across the Nara Basin strongly align with Senda’s conclusions. The critical point here is that, during at least the Kofun period, much of the northern and central basin—apart from a few exceptions—remained marshy or underwater, thus unsuitable for wet-rice agriculture, the main economic activity of people in Yamato during the Kofun period. This realization is key to understanding ancient Japanese history. For the same reason, Kofun-period settlers did not colonize the Kyoto Basin (modern Kyoto City).

Consequently, people arrived successively from many regions in southern Yamato, an area suited to wet-rice agriculture, and competition intensified over land that had long been worked by those practicing dry-field agriculture, including millet farming. The condition that made the land valuable, its suitability for paddies, drove the contest. My personal research has clearly demonstrated that some of the people who had lived there left their homeland and dispersed widely.

Thus, during the late Yayoi period, intense conflict erupted among diverse groups of differing origins vying for control within a confined area. These conflicts are directly connected to the origins of the imperial lineage, but what mattered was not difference of origin. What drove the turmoil was the condition of the place, a southern basin with limited land fit for paddies, and the structure of power that gathered there.

The earliest written records documenting this chaotic situation in the southern Nara Basin appear in the Chinese historical text Gishi Wajinden (魏志倭人伝), part of the Records of Wei. Amid this turmoil, Himiko (卑弥呼) ascended temporarily as queen to mediate the chaos. From this perspective, I argue that Himiko was an ancient shamaness (miko, 巫女) who was called in from outside this contest and who carried rites rooted in the land. Another essential factor explaining why the dominant groups of later times did not relocate their political centers onto the former Lake Yamato’s wetlands relates to a long-standing Japanese concept—the negative ki (気) associated with marshlands. Rooted in ancient Chinese wisdom related to feng shui (風水), these ideas deeply influenced early Yamato’s founding.

While this summary simplifies many complex issues, it provides the foundation necessary for understanding the Mononobe clan, which I will examine further in the next article. A crucial point moving forward is recognizing that the Mononobe did not simply vanish due to defeat by the Soga clan—an insight we will explore next time.