Catania has been a prized possession of numerous empires over the years, from the Greeks to the Romans to the Arabs to the Normans to the Spaniards. However, its people face a more hazardous foe right in their backyard: Mount Etna, Europe's largest and most active volcano, which devastated the city in 1693 with earthquakes and lava flows. If you look attentively at the baroque buildings built following the eruption, you'll see a clever utilization of lava.