Then came in all the king’s wise men - The classes above referred to, Daniel 5:7.
But they could not read the writing - The character was an unknown character to them. It may have been a character which was not found in any language, and which made the power of Daniel to read it the more remarkable, or it may have been, as suggested in the notes at Daniel 5:7, a foreign character with which they had no acquaintance, though familiar to Daniel.