Machaerus means in the bible: Perea fortress, located above the northeastern coast of the Dead Sea. Although it isn’t mentioned in the New Testament by name, Josephus Antiquities 18.5.1-2 refers to it as the location where John the Baptist, who was beheaded and imprisoned there, like in Matt. Mark 6:17-17, 28. There are still some ruins at the site.
(in Bible Dictionary)