Song dynasty historian Sima Guang in the Zizhi Tongjian: In 665, Emperor Gaozong and his powerful wife Empress Wu went to Luoyang and began preparation in earnest to make sacrifices to heaven and earth at Mount Tai – a traditional ceremony for emperors that were rarely carried out in history due to the large expenses associated with them. At Empress Wu's request—as she reasoned that the sacrifice to earth also included sacrifices to past empresses (Emperor Gaozong's mother Empress Zhangsun and grandmother Duchess Dou, posthumously honored as an empress), she believed that it would be more appropriate to have females offer the sacrifices rather than male officials, as had been tradition in the past. Emperor Gaozong decreed that the male ministers would offer sacrifices first, but Empress Wu would next offer sacrifices, followed by Princess Dowager Yan, the mother of Emperor Gaozong's younger brother Li Zhen the Prince of Yue. In winter 665, Emperor Gaozong and Empress Wu and headed for Mount Tai. On the lunar new year (10 February 666), he and she initiated the sacrifices to heaven, which were not completed until the next day. On 12 February, sacrifices were made to earth. He and she gave general promotions to the imperial officials, and it was said that starting from this time, promotions of imperial officials, which were strict and slow during the reigns of Emperors Gaozu and Taizong, began to become more relaxed and often excessive. He and Empress Wu also declared a general pardon, except for long-term exiles. Japan, India, the Persian court in exile, Goguryeo, Baekje, Silla, the Turks, Khotan, the Khmer, and the Umayyad Caliphate all had representatives attending the Feng and Shan sacrifices held by Emperor Gaozong and Empress Wu in 666 at Mount Tai. Qianfeng and Zhongzhang eras (666–670) In summer 666, Yeon Gaesomun died and was initially succeeded as Dae Mangniji by his oldest son Yeon Namsaeng. As Yeon Namsaeng subsequently carried out a tour of Goguryeo territory, however, rumors began to spread both that Yeon Namsaeng was going to kill his younger brothers Yeon Namgeon and Yeon Namsan, whom he had left in charge at Pyongyang, and that Yeon Namgeon and Yeon Namsan were planning to rebel against Yeon Namsaeng. When Yeon Namsaeng subsequently sent officials close to him back to Pyongyang to try to spy on the situation, Yeon Namgeon arrested them and declared himself Dae Mangniji, attacking his