Did you ever wonder who first said “When in Rome, do as the Romans do?”  The following source explains: http://www.italiannotebook.com/local-interest/origin-do-as-romans-do/

Do you know the expression’s origin? St. Ambrose, way back in 387 A.D.

As the story goes, when St. Augustine arrived in Milan to assume his role as Professor of Rhetoric for the Imperial Court, he observed that the Church did not fast on Saturdays as it did in Rome.

Confused, Agostino consulted with the wiser and older Ambrogio (Ambrose), then the Bishop of Milan, who replied: “When I am at Rome, I fast on Saturday; when I am at Milan I do not. Follow the custom of the Church where you are.”

In 1621, British author Robert Burton, in his classic writing Anatomy of Melancholy, edited St. Ambrose’s remark to read: “When they are at Rome, they do there as they see done.”

Down through the years, Burton’s turn of the St. Ambrose quote was further edited, anonymously, into what is widely repeated today on a daily basis by some traveler, somewhere, trying to adjust to his/her new or temporary surroundings.