Roman Empire

Ancient Roman concrete lasts 2,000 years by healing itself. In 2023 MIT found the lime specks in it were deliberate, not careless. When water enters a crack, the lime dissolves into calcium that reacts with CO2, sealing it as Calcium carbonate.

The British Empire—the largest in history, covering a quarter of Earth's land and people—never had an emperor. In Europe, the title required Roman Empire succession, but Britain had no Roman ties, and Henry VIII's split with the Pope sealed the impossibility.