Purim costumes and the Italian carnival influence
1500
Bibliographer Moritz Steinschneider theorised that the custom of masquerading in costumes and wearing masks on Purim originated among Italian Jews at the end of the 15th century, influenced by the Roman carnival, since Purim usually coincides with Mardi Gras. A recurring annual custom. NOTE: the theory is contested, Rabbi Yair Hoffman argues Steinschneider was mistaken, and cross-dressing at Purim is already referenced by Kalonymus ben Kalonymus in the early 14th century.
Source: Wikipedia
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