延慶改元・改暦への鎌倉幕府の関与について : 『大唐陰陽書』付載文書の検討をてがかりにして

延慶改元は徳治三（一三〇八）年の後二条天皇の死去と花園天皇の践祚を契機に行われた。延慶改元は鎌倉幕府が天皇の管轄事項である改元に関与した例とされるが、従来、改元の問題は即位過程の中で実施された改暦と切り離されて論じられてきた。島津家本『大唐陰陽書』に付載された伏見上皇院宣と得宗北条貞時書状は、延慶改暦に功のあった宿曜師宣算を褒賞したものである。本稿では、これと花園天皇の即位に到る過程、および朝廷への窓口である六波羅探題金沢貞顕による公家からの典籍の借用・書写・収集からうかがえる人的交流をリンクさせることで、改元・改暦をめぐる公武交渉の実態を検討した。花園天皇の即位に際して選定された「延慶」は、伏見院の主導で関東申次西園寺実兼らの意向を反映していた。一方、即位の日取りの設定には凶例とされる中間朔旦冬至が問題であった。先例とされた保元改暦は、鳥羽上皇没後の保元の乱の発生が背景にあったことをみると、延慶改暦は乱の発生を回避する願望があった可能性がある。一方、貞顕による典籍の書写・収集活動は、彼の文化的営為を知る目的で研究されてきたが、その書写先には大覚寺統の公家や改元・改暦に関わった人物との交流が濃厚である。書写活動には公家からの情報収集などの目的が潜んでいただろう。また、後年の貞顕書状には延慶元年の改元・改暦の時期に東使が在京していたために自身の鎌倉下向がかなわなかったとある。これは、東使二階堂貞藤・長井貞広が上洛して花園天皇の奏事始にいたる交渉、長崎思元が関与した改元・改暦完了後の建長・円覚両寺を定額寺とする一件と円覚寺扁額の拝領という二つの事態をさしていよう。右の事情を勘案すると、即位以前の改元と批判された延慶改元と鎌倉幕府の関与を強調する公家の態度は、中間朔旦冬至の回避を前提に即位・改元の日取りに合意した伏見院と得宗北条貞時の立場を反映していると考えることができる。

The era name was changed to Enkyō in Tokuji 3 (1308), when Emperor Gonijō died and was succeeded by Emperor Hanazono. This incident was referred to as an example of interferences of the Kamakura Shogunate with the era name change, which fell within the exclusive competence of the emperor, although most past studies discussed the era name change separately from the calendrical reform made at that time as part of the enthronement process. Ex-emperor Fushimi and Tokusō Hōjō Sadatoki praised Sensan, a master astrologer, for his contribution to the calendrical reform to Enkyō in their letters, respectively, which were appended to the Shimazu family's copy of Daitō Inyōsho (the Book of Yin and Yang in the Tang Era). This study analyzes this calendrical reform in relation to the process of enthronement of Emperor Hanazono and in comparison to the personal networks reconstructed by examining which Court nobles Kanesawa Sadaaki, appointed to Rokuhara Tandai as a liaison to the Imperial Court, borrowed, copied, and collected books from to elucidate the actual negotiations between the Imperial Court and the Shogunate on the era name change and the calendrical reform.Enkyō was chosen as the name of the first era of the reign of Emperor Hanazono, reflecting the opinions of Court nobles such as Saionji Sanekane, Kantōmōshitsugi (a liaison to the Kamakura Shogunate), under the leadership of Ex-emperor Fushimi. Meanwhile, that year's winter solstice coincided with a new moon, breaking the coincidence cycle of 19 years, and this was seen as a bad omen. The fact that at the time of the calendrical reform to Hōgen, which formed a precedent, the War of Hōgen broke out after the death of Ex-emperor Toba implied that the calendrical reform to Enkyō may have been related to the wish to avoid war. On the other hand, the studies of Sadaaki's collection and transcription of books aimed to elucidate his cultural activities but also revealed that through these activities, he is highly likely to have interacted with Court nobles of the Daikakuji lineage and other people involved in the determination of the era name change and the calendrical reform. His transcription activities may have been secretly aimed at collecting information from Court nobles. Moreover, according to a letter he later wrote, he could not go to Kamakura because Tōshi messengers dispatched from the Kamakura Shogunate stayed in the capital city at the time of the era name change / calendrical reform in Enkyō 1 (1308). This could refer to the following two issues: (1) the dispatch of Tōshi messengers, Nikaidō Sadafuji and Nagai Sadahiro, to the capital city to negotiate details about the enthronement of Emperor Hanazono and (2) the involvement of Nagasaki Shigen in negotiations to grant Kenchō-ji and Engaku-ji temples the status of Jōgakuji after the era name change / calendrical reform and bestow a signboard on the latter temple. In light of the above, it can be assumed that the era name change to Enkyō, which was criticized for preceding the enthronement, and Court nobles' attitudes that emphasized the interferences of the Kamakura Shogunate may have reflected not only the political stance of Tokusō Hōjō Sadatoki but also the agreement of Ex-emperor Fushimi to set the dates of the enthronement and the era name change to avoid the irregular coincidence of the winter solstice and moon cycles.

source:https://www.rekihaku.ac.jp/outline/publication/ronbun/ronbun9/index.html#no212