Ancient engineering gets tested against the physical evidence in this four-episode series, each installment built around one structure and the puzzle of how a pre-industrial society actually built it. The first episode follows how ancient Egyptians moved and raised granite monoliths weighing up to 500 tons, weighing nautical transport methods against the manpower and rope technology available at the time. On Easter Island, the focus shifts to the moai, the massive stone heads carved by a vanished island culture, and the theories linking their construction to the island's ecological collapse. A third episode walks through the ruins of Roman public baths, using the surviving plumbing and heating systems to reconstruct the daily routines of Roman citizens. The final episode examines the Rainbow Bridge of 12th-century China, an arched wooden span built without nails, and the carpentry logic that let it hold. Each episode leans on engineers and archaeologists working from the physical remains rather than written records to explain how the work got done.