The Three Ritual Classics have always been difficult to read, their language is archaic, their text is brief, and they are known to be difficult to understand,[4] For example, many of the architectural structures and scales of the palaces in the Book of Rites have not been covered, and they have been "repeatedly changed over the ages, gradually becoming different from the old", so that when reading the Rites, the palaces of the Son of Heaven and Lords are often imagined to be a castle in the sky.