《汉书·志·五行志中之下》
过去夏都河东，殷都河内，周都河南洛阳，河、洛出现图、书，秦都于渭水之阳，而渭水几次变红，这都是嘉瑞异象与德相应的验证啊。
昔三代居三河，河洛出图书，秦居渭阳，而渭水数赤，瑞异应德之效也。
In the past, the Xia capital was in Hedong, the Yin capital was in Henan, and the Zhou capital was in Luoyang, Henan. The He and Luo rivers both showed auspicious signs and writings. The Qin capital was to the north of the Wei River, and the Wei River turned red several times, all of which were auspicious signs in response to virtue.