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…that they were called the Phlegraean Plains, from their flames and burning; (for so the word signifies.) But Cornel. Strabo calls it, Vulcan’s open Market place (publick Theater or Court.) For in manner of a huge Theater, as it were, it sends forth perpetual fires; and begets much Sulphur and combustible and inflammable matter, and therefore called…
https://www.wichita.edu/academics/fairmount_las/geology/wparcell/Kircher/volcanoes/chapter5.php