《后汉书·列传·陈王列传》
诸侯上象二十八宿，垂象在天，下应分土，藩屏王室，汉高祖约法，不是功臣不得封侯。
夫诸侯上象四七，垂耀在天，下应分土，籓屏上国。高祖之约，非功臣不侯。
The vassal states take the form of twenty-eight constellations, their influence extending to the heavens and affecting the territory below. They act as screens to the royal family. As Han Gaozu established laws, non-meritorious subjects could not be granted a title of Marquis.