Three (more) Forgotten Roman Megaprojects

Last year, I made a video about spectacular feats of Roman engineering that most people have never heard of. This sequel explores three more megaprojects as impressive in their way as the Pantheon and Colosseum. Number three, Spain's Hollow Mountain. For centuries, the Roman Empire's richest gold mines were in Spain. Miners followed gold-flecked rivers deep into the mountains, searching for nuggets, sifting through alluvial deposits, and driving tunnels to mother loads. Operations in the Spanish mines were on a scale not exceeded until the Industrial Revolution. Pliny the Elder describes labyrinths of shafts and adits lit by smoky lamps, where men labored with picks and hammers, used fires and vinegar to fracture stone, and pulverized ore with crushing machines. Creaking rows of wooden scoop wheels, operated day and night by teams of slaves, kept groundwater from filling the works. The most awe-inspiring Roman mine in Spain was located at a site known as Las Medulas, where streams flowing down from the Somiedo Mountains left gold-rich alluvial deposits. In many places, however, up to 100 meters of sediment that contained little gold covered the oriferous strata. To expose them, the Roman miners used the power of water. No fewer than seven aqueducts, each 2 to 3 meters wide and up to 50 kilometers long, were built along the mountain ridges above the site. Together, they delivered an estimated 34 million liters every day. Some of the water was directed over the deposits in a continuous stream, loosening and washing away the overburden. This method, analogous to the hydraulic mining used during the California and Yukon gold rushes, left a web of gullies still visible below the site. Water was also collected in reservoirs on the rim of the mine. At intervals, their sluice gates were opened, unleashing floods that washed huge quantities of sediment downslope. Pliny describes this technique as ruina montium, the destruction of mountains. The effects were dramatic. Whole hillsides disintegrated in a pandemonium of rushing water and tumbling stones, compressing a thousand years of erosion into seconds. The debris avalanched to the base of the site, gradually filling a natural valley. The mines at Las Medulas remained in operation for centuries. By the time work stopped in late antiquity, a whole range of hills had been washed away, leaving a lunar landscape of gullies and ridges that bears silent witness to the Roman thirst for gold. Number two, the wall that stopped the nomads. North and west of Constantinople lay the Plains of Thrace, a fragment of the Great Steppe that stretches from the Black Sea to Mongolia. Periodically, nomadic peoples erupted from the grasslands to challenge the Roman frontier along the Danube. The most notorious invaders were the Huns, but soon after the collapse of Attila's empire, a new people, the Bulgars, began to raid Thrace. To contain their incursions, Emperor Anastasius I built a wall 65 kilometers west of Constantinople. This fortification, known as the Anastasian Wall or the Long Wall of Thrace, ran 46 kilometers from the Black Sea to the Sea of Marmara, protecting the imperial city and its fertile hinterland. Built of large stones bonded with mortar, the wall was more than three meters thick and may have stood 10 meters high. It was studded with enormous polygonal towers, designed to provide platforms for artillery. Between these bastions were more than 300 rectangular towers, which housed guards and gave access to the parapet. Small forts were located behind the defenses at intervals of about three and a half kilometers. A ditch 15 meters wide guarded the wall's outer face. Though shorter than Hadrian's Wall, the Anastasian Wall was more impressively fortified and reflected the latest advances in late antique military architecture. Unlike Hadrian's Wall, however, it seems to have never been adequately garrisoned. It was breached by nomads several times, most dramatically in the last years of Justinian's reign, when the aged general Belisarius beat back the cut-rigger Bulgars with a ragtag army of peasants and conscripts. Thereafter, the wall was allowed to crumble. Much of its stone was pillaged for reuse, and today, only a few short segments survive of New Rome's last defense. Number one, the harbor that fed Rome. The city of Rome is about 20 kilometers from the sea. Although the Tiber was deep enough to be navigated by small boats, sandbars and strong currents made the river treacherous for seagoing vessels, which had to dock at Ostia. As Rome grew into the ancient world's largest city, reliant on provincial grain and hungry for imported luxuries, Ostia's harbor became increasingly inadequate. Many ships, including the huge transports of the Egyptian grain fleet, were forced to land at Putioli on the distant Bay of Naples. Claudius, who became emperor in the midst of a grain shortage, decided to build a new harbor, known simply as Portus, the port, just north of Ostia and the Tiber mouth. Construction lasted almost 20 years. The first challenge was excavating a vast basin, large enough for hundreds of ships, from the marshes and sandhills along the shore. Two curving breakwaters were built to protect the basin from the winds and current. A gargantuan ship, used to transport the obelisk now in St. Peter's Square from Egypt, was scuttled alongside one of the jetties and filled with concrete to serve as the foundation of a four-story lighthouse modeled on the pharaohs of Alexandria. For all its size and convenience, Claudius' harbor did not offer full protection from the weather. A sudden squall in 62 AD kicked up high waves inside the harbor basin, sinking 200 ships. Portus only became weatherproof a half-century later, when Trajan constructed an inner harbor. The new basin, a hexagon 358 meters to a side, was equipped with numbered mooring blocks, ringed by multi-story warehouses, and overlooked by a colossal statue of Trajan. A short distance away, a monumental palace was constructed, complete with an amphitheater, baths, and lavish reception rooms. Though probably intended for the procurator who oversaw the harbor, it may have been used by the emperor himself on periodic visits. Trajan's extension of the harbor at Portus was an immediate success. The grain fleet was diverted from Puteoli to the hexagonal basin, and the canals connecting Portus with Ostia and the Tiber bustled with boats carrying goods upriver to Rome. The town that grew up around the warehouses and quays quickly eclipsed Ostia. Portus thrived as long as Rome did, but when trade dwindled and the imperial city's population collapsed, the vast harbor became redundant. The basins were choked with sand and silt by the early Middle Ages. The original Claudian harbor is now covered by a Fiumicino airport, but Trajan's hexagonal basin, refilled a century ago, is visible from every international flight that lands in Rome. All you have to do is look down. The Romans left many other wonders across their empire, and I've been fortunate enough to encounter some of them on my travels. On a recent visit to Tunisia, I explored the longest Roman aqueduct ever constructed. To watch my video on that forgotten megaproject, follow the link on screen and in the description. My new book, Insane Emperors, Sunken Cities, and Earthquake Machines, is now available as a paperback, ebook, and audiobook. 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