Roman Concrete Revolutionizes Construction

Roman concrete (opus caementicium) used volcanic ash from Pozzuoli that actually grows stronger with age — the opposite of modern concrete, which degrades. This technology made possible the aqueducts, harbors, temples, and public buildings that defined Roman cities across the empire. The Pantheon's unreinforced concrete dome, completed shortly after this era, remains the world's largest. Every city Paul would later visit owed its infrastructure to this innovation.