Why do the windows have bars on them? And why don't the windows have any glass to keep the cellar warm in the winter? Both of these are common questions asked by visitors when they tour Montpelier's cellar. The bars, colloquially known as "pig bars", were commonly found on cellar windows throughout the former British colonies in America. Their purpose was to keep people, as well as other animals like raccoons, opossums, chickens and most other creatures, out of the cellar and away from the valuable food and supplies stored there.