The Machaerus fortress was erected on a prominent hill about 32 kilometers southwest of Madaba. The mikveh ritual bath and immersion pool used for purification were apparently built for the Herod royal family's personal use.A long article with lots of background on Machaerus. Past PaleoJudaica posts on Machaerus are here and here.
The bath is the biggest of its kind ever found in Jordan. It boasts 12 steeps and a reserve pool containing water to fill the pool when its water ran low.
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