Tom Nealon examines the history of butter:
There is no evidence that the Romans used butter in their cuisine, (no form of butter appears in the ancient Roman cookery book Apicius) preferring olive oil, but used pure butter “medicinally”, including for making the skin “pliable” and in other situations that are too easy to imagine to be described here. ... Impure butter was viewed by the Greeks and Romans as a sure sign of barbarism and an invitation to be “civilized.” ... It was only after the fall of Rome that it slowly became acceptable to eat butter in polite company. By the Middle Ages, German and French butter fanatics would actually bribe their priests to allow them to eat butter during Lent, until, under pressure from the pro-butter Protestants, the Catholic Church allowed the consumption of butter during Lent during the 16th century.