The Pantheon has stood in Rome for nearly 2,000 years, its concrete dome outlasting every modern equivalent. For centuries, engineers blamed the white chunks in Roman concrete on sloppy mixing. In 2023, MIT found the opposite: those "lime clasts" are the secret. When a crack forms and water seeps in, they react and recrystallize to seal it - the concrete heals its own cracks, 2,000 years before we understood the chemistry.
