Roman concrete has been underwater for two thousand years in some locations and is stronger now than when it was poured. This is not a figure of speech. The concrete used in Roman harbor structures — the piers, breakwaters, and seawalls built along the Mediterranean coast during the Republic and Empire — has been studied by geologists and materials scientists who have found that it has been gaining strength over time rather than degrading, a property that modern Portland cement concrete does not share. Understanding why this happens has become one of the more productive intersections of archaeology, geology, and materials science in recent decades, and the answer reveals something important about Roman empirical knowledge and its limits.

The Romans mass-produced glass. This statement requires emphasis because it contradicts the common assumption that mass production is a modern phenomenon and that ancient luxury goods were necessarily handmade in small quantities by skilled artisans serving elite clients. Roman glass was made in those ways too — the cameo glass of the Portland Vase, the intricate millefiori bowls, the delicate cage cups — but alongside and beneath these luxury productions existed a glass industry of genuinely industrial character, producing standardized vessels in enormous quantities for the ordinary consumer market that constituted the overwhelming majority of Roman commercial glass transactions.

Rome’s mines were among the most productive and the most deadly operations in the ancient world. The silver mines of Spain, the gold mines of Dacia, the iron mines of Noricum, the lead mines of Britain, the copper mines of Cyprus — across the empire’s territories, Roman exploitation of mineral resources operated at a scale and intensity that would not be matched in Europe until the Industrial Revolution. The quantities extracted were enormous, the methods often technically sophisticated, and the human cost on the enslaved and condemned workforce was catastrophic in ways that the ancient sources acknowledge with varying degrees of discomfort.