The origins of the bagpipe can be traced back to the most ancient civilizations. They have always been made in many shapes and sizes, and have been played throughout Europe from before the Norman Conquest until the present day. Bagpipes are a class of musical instrument, aerophones, which is any musical instrument producing sound primarily by causing a body of air to vibrate, without the use of strings or membranes, and without the vibration of the instrument itself adding considerably to the sound. The Scottish Great Highland Bagpipe and the Irish uilleann pipes are probably the best known variety and have the greatest international visibility. In the United Kingdom and Commonwealth Nations such as Canada and New Zealand, the bagpipe is commonly used in the military and is often played in formal ceremonies. Bagpipes have often been used in various films depicting moments from Scottish and Irish history; the feature film Braveheart and the theatrical show, Riverdance, have served to make the Uilleann pipes more commonly known.