Why was Dantes thrown in the dungeon with the mad people?

Dantes threatened a guard.

“Threats!” cried the jailer, retreating and putting himself on the defensive; “you are certainly going mad. The abbé began like you, and in three days you will be like him, mad enough to tie up; but, fortunately, there are dungeons here.”

Dantès whirled the stool round his head.

“All right, all right,” said the jailer; “all right, since you will have it so. I will send word to the governor.”

“Very well,” returned Dantès, dropping the stool and sitting on it as if he were in reality mad. The jailer went out, and returned in an instant with a corporal and four soldiers.

“By the governor’s orders,” said he, “conduct the prisoner to the tier beneath.”

“To the dungeon, then,” said the corporal.

“Yes; we must put the madman with the madmen.” The soldiers seized Dantès, who followed passively.