Carl Pyrdum of Got Medieval (with a little help from Mario) makes a clever argument for the illustration of gravity in the margins of medieval manuscripts:
In order to keep the man and his goat in the middle from falling right on through the bottom of the page, the artist draws in little patches of ground beneath them. Mario, no stranger to platforms that hang in the air as if bolted to the background, would feel right at home with this arrangement.
See the original blog post here.