It is Saturday afternoon. Liu Tao and his friend David are taking a walk in the park. There are many public signs in it. They mean different things. Liu Tao knows a lot of things about them. Suddenly, they see a short man walking on the grass. Liu Tao points to the sign on the grass and says to him, "Sir, look at the sign! You can't walk on the grass. "The man smiles and says, "You are right, young man. But I'm the park keeper. I'm looking after the grass. "

一位导游在巴黎卢浮宫博物馆介绍某一历史文物时说：“石柱上的法典是迄今所知世界上第一部比较完备的成文法典。”你知道这位导游介绍的文物是什么吗？（    ）