The Roman patrons of the arena and their modern counterparts sat and sit on stone blocks. Those stone blocks are limestones, probably of Jurassic age, in which ammonites are readily visible (there's a good example at the bottom center of the image below). Ammonites were coiled molluscs with internal chambers, analogous to the modern chambered Nautilus. Like dinosaurs, another group of famous Jurassic organisms, ammonites went extinct at the end of the Cretaceous. Sixty-six million years later, their remains support the posteriors of theatre viewers in Verona.