Gypsum would be a much simpler name than plaster of Paris.
But English artisans of the fourteenth and fifteenth century thought the best quality of gypsum for conversion into plaster and mortar came from the large deposits in the region of Montmartre on the outskirts of Paris, and thus insisted upon plaster of Paris.
The name remains, but has long been applied to any calcined gypsum, regardless of place of origin.
