17 events the sources record for this year, grouped by region.
What happened
China (1)
In the third month, guard-barrier envoys (kokanshi) were dispatched to Ōmi, Mino, Ise and others. (Shoku Nihon Kōki 續日本後紀 卷第二十 (원문 41번째 단락))
Japan (16)
In the third month, on day 己亥, Emperor Ninmyō dies at the Seiryōden; Crown Prince Michiyasu (Montoku) receives the divine seal and a precious sword and moves to the Tōgū Aen. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 3月)
In the third month, on day 癸卯, following the edict, Emperor Ninmyō is buried frugally at the Fukakusa mausoleum. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 3月)
In the third month, on day 乙巳, a storm with thunder topples trees at the Saga mausoleum; Chūnagon Abe no Yasuhito is sent to inspect it. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 3月)
In the fifth month, Prince Shimae and others are sent to the Ise Grand Shrine to receive the Saiin imperial princess (saigū). (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 5月)
In the fifth month, on day 辛巳, Empress Dowager Tachibana no Kachiko, widow of Emperor Saga, dies; the next day she is buried simply at Mount Fukatani. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 5月)
In the fourth month, on day 甲子, Emperor Montoku ascends the throne at the Daikyokuden; on the previous day, 癸亥, the accession is reported to the Fukakusa mausoleum. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 4月)
In the sixth month, on day 甲戌, Dewa province, saying its border touches the Emishi and it is always in turmoil, requests one onmyōji (diviner) and is permitted. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第一 「嘉祥三年」 6月)
In the eighth month, on day 癸丑, Prince Kusuno and others are sent to the Ise Grand Shrine to report that Princess Anshi has become saiō. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第二 「嘉祥三年」 8月)
In the seventh month, on day 己亥, heavy rain collapses the twelve-jō ryūbidō (dragon-tail stone stairway) in front of the Daikyokuden. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第二 「嘉祥三年」 7月)
In the ninth month, on day 壬午, palace priest Urabe no Osada and others are sent to Settsu to hold the Yasoshima rite; the same day a white tortoise is obtained in Settsu and presented. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第二 「嘉祥三年」 9月)