Why Roman concrete still stands strong while modern version decays

Scientists have cracked the secret to Roman water-based structures' strength - and findings could help today's builders

Their structures are still standing more than 1,500 years after the last centurion snuffed it: now the Romans' secret of durable marine concrete has finally been cracked.

The Roman recipe - a mix of volcanic ash, lime (calcium oxide), seawater and lumps of volcanic rock - held together piers, breakwaters and harbours. Moreover, in contrast to modern materials, the ancient water-based structures became stronger over time.