Montressor chains Fortunato using the bolts in the wall. While Fortunato is passed out from his intoxication Montressor Bricks the Archway up. The last thing he hears is the ringle of bells.
Montressor continued to build the brick wall and when there was one final brick left he stuck the torch in the hole to see Fortunato one more time. And Fortunato thought it was a joke and pleads for Montressor to get him out.
Montressor covers the brickwork with bones and walks away. While walking away Montressors heart drops but it wasn't because of the deed he has done it was because of the moisture in the catacombs. He goes on to explain no has found Fortunato's body for a century and a half.