He got drunk and ordered his servants to bring in the gold and silver cups his father Nebuchadnezzar had taken from the temple in Jerusalem. Belshazzar wanted the cups, so that he and all his wives and officials could drink from them.
Herod had earlier arrested John and had him chained and put in prison. He did this because John had told him, “It isn't right for you to take Herodias, the wife of your brother Philip.”