[1] In 378 BC the states of Han, Zhao, and Wei invaded Qi and attacked the city of Lingqiu (in present-day Gaotang County, Shandong Province).
[1][2] Because of the lack of reliable records during the Warring States period, the chapter on the House of Tian in Sima Qian's influential Shiji is unreliable and error-prone.
Yan's reign was completely omitted from the Shiji, and he remained largely unknown until the discovery of the Bamboo Annals in 281 AD during the Jin dynasty.
However, archaeologists have concluded that they are in fact the tombs of Yan and his brother and murderer, Duke Huan of Tian Qi.
[3] Since 2008 they have been included in the tentative list of UNESCO World Heritage Sites as part of the ancient Qi capital and mausoleum complex.