12 events the sources record for this year, grouped by region.
What happened
China (4)
Zhang Yichao sent his elder brother to present the registers of eleven prefectures, including Gua, Sha, Yi and Su. He and Long had fallen to Tibet over a hundred years earlier, and Longyou was recovered. (Old Book of Tang (Jiu Tangshu), Annals 舊唐書 卷18下 大中5年)
Zhang Yichao, a native of Shazhou, presented eleven prefectures including Guazhou and Shazhou to the court. (New Book of Tang (Xin Tangshu), Annals 新唐書 卷008 穆宗~宣宗 大中5年10月)
In the second month, on day 丙辰, the Seiryōden where the late emperor rested is moved and made into the Buddhist hall of Kashō-ji; the reigning emperor could not bear to use it. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第三 「仁壽元年」 2月)
In the fourth month, on day 庚午, the era is changed to Ninju; in the first year of his reign, the era is changed citing omens of a white tortoise and sweet dew. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第三 「仁壽元年」 4月)
In the eighth month, on day 甲寅, a kebiishi (inspector) is sent to distribute grain to the people of the capital hit by flood; earlier, on day 己酉, there was heavy rain. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第三 「仁壽元年」 8月)
In the eighth month, on day 乙丑, the Saiin princess of Ise purifies herself at the Kamo River and enters Nonomiya the same day, in preparation for the Daijōsai. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第三 「仁壽元年」 8月)
In the tenth month, on day 甲子, the emperor visits the Kamo River and greatly carries out the misogi purification rites before the Daijōsai. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第三 「仁壽元年」 10月)
In the eleventh month, on day 辛卯, rites are held at the Hasshōin for the Daijōsai, followed by a banquet at the Buraku-in. (Nihon Montoku Tennō Jitsuroku 日本文德天皇實錄 卷第三 「仁壽元年」 11月)
Western Europe (2)
King Æthelstan and Ealhere fought at Sandwich by sea, killed a great host, and captured nine ships. (Anglo-Saxon Chronicle Giles/Ingram 1847 A.D. 851 항 (pg657.txt 줄 2612))
Heathens wintered on the island of Thanet for the first time. (Anglo-Saxon Chronicle Giles/Ingram 1847 A.D. 851 항 (pg657.txt 줄 2612))