《史记·三十世家·魏世家》
八年，秦昭王亲自称西帝，齐湣王自称东帝，过了一个多月，都重新称王收回了帝号。
八年，秦昭王为西帝，齐湣王为东帝，月馀，皆复称王归帝。
In the eighth year, King Zhaoxiang of Qin personally proclaimed himself Emperor of the West, and King Min of Qi proclaimed himself Emperor of the East. After more than a month, they both resumed the title of king and withdrew the title of emperor.