Notas del episodio
For centuries engineers admired the slight upstream curve of the Pont du Gard in southern France as a deliberate brace against floods, until a 1989 micro-topographic survey showed it was deformation from 2,000 years of sun heating one side of the stone. The aqueduct bridge carried water to Nemausus, modern Nîmes, which needed an estimated 40,000 cubic meters a day. The springs at Fontaine d'Eure near Uzès sat only about 20 kilometers away, but the Garrigues hills forced a winding 50 kilometer route with just 17 meters of total drop, an average gradient of 1 in 3,000, surveyed with the water-filled chorobates and the groma. Coins of Emperor Claudius now date construction to roughly 40 to 60 AD, not to Agrippa.
Up to a thousand men spent about 15 years moving over 50,400 tons of limestone from a quarry 700 meters downstream, with blocks of up to six tons set without mortar and marked with directions like fronte dextra. Hard water later laid down calcium deposits up to 50 centimeters thick, and when Rome could no longer pay its maintenance crews the channel choked and stopped by the sixth century. The bridge survived as a toll crossing, was cut away in the 1620s by the Duke of Rohan to move artillery, got a side road bridge from Henri Pitot in the 1740s, and was restored under Napoleon III in the 1850s.
- The interior waterproofing called maltha, made from slaked lime, pork grease, and the latex juice of unripe figs
- Why the lowered bridge height forced a stretch where the channel drops only 7 millimeters per 100 meters
- How roots, algae, and bacteria sped up the calcium buildup in a process called biolithogenesis
- The cost of about 30 million sesterces, and why later aqueducts at Segovia used slender piers instead
- Alexandre Dumas' fury at the added road bridge, Rousseau feeling like an insect in 1738, and the 2000 project that removed cars and shops