The short answer is: dust, dead plants, and debris. The videos in this series answer viewer questions about the Ancient Greeks and Romans in a few minutes. If you have a question that the classical world that you’d like to see addressed, feel free to let me know in the comments. If you enjoy this series, you might be interested in my forthcoming book “Naked Statues, Fat Gladiators, and War Elephants: Frequently Asked Questions about the Ancient Greeks and Romans,” now available for preorder: