A hazy history of Roman Portugal – Part 6 – The economy

Rudimentary forms of surface mining and metallurgy had been a mainstay of the economy since Chalcolithic times. Bronze and copper objects were exported to markets as far away as the Danube, while silver was shipped in large quantities to countries in the eastern Mediterranean. The arrival of the Romans brought new technology that allowed for an increase in production to meet both domestic demand and Rome’s demand for the payment of tribute.

The alternative to surface mining was deep mining which, although more difficult and dangerous, promised better returns for gold and silver mining. A series of narrow exploration wells were dug to a depth of 50 m. until a mineral vein is encountered. The shaft would then be widened so that horizontal galleries could be opened and the ore hoisted by pulleys to the surface. The lifting mechanism was controlled by large wheels up to 5 m. diameter in holm oak and manually operated.

Aqueducts were built to bring water from the dyked rivers to cisterns which then set off a powerful flow through the surface mines to loosen the rocks. Machines called “stamp crushers” and “hammers” were also fed by this stream and used to grind the ore to extract the metals.

Manual labor was carried out almost exclusively by slaves, some of whom were prisoners or hostages taken from the Lusitanian tribes while others were brought from various provinces of the Roman Empire. The working conditions were appalling, only leather aprons and hoods were provided for protective clothing, while the underground tunnels were dimly lit by oil lamps installed in niches. Roof falls were common, especially when Roman supervisors deliberately started fires to loosen ore. The only tools available were stone hammers and iron picks. No wonder that the average age of slaves ‘mortality is around 25, as the few epitaphs found in the cemetery of the workers’ compound attest.

Much of the mining took place in the Iberian Pyrite Belt which covered a large geographic area stretching from Alcaçer do Sal to Seville with the main mining towns of Aljustrel, Castro Verde, Neves Corvo and Mertola. In the north, by far, the largest mining operation took place in Três Minas, located near Vila Pouca de Aguiar in the Serra da Pedala. It was perhaps the largest gold mine in Iberia with enormous production that was used almost exclusively to improve Imperial chests. The extent of such production can be measured by calculating slag heaps of 18 million tonnes at Três Minas and 3 million at Aljustrel; staggering figures when you admit that everything was driven by manual labor

All mining in Roman Portugal was state controlled, with army detachments stationed in all major centers. The movement of processed minerals was by railcar with protection of the cavalry against bandits and severe penalties were imposed for theft either in transit or on site. For Aljustrel and some smaller sites, a concession system has been authorized with an exploration royalty paid initially and a production share (typically 50%) of any ore successfully mined. These and other regulations were notoriously recorded on two brass plates discovered in the Aljustrel slag. Other written records are scarce, and accurate industry assessments are largely conjecture based on the relatively low degree of archaeological excavation which has revealed an abundance of small sites where lead, tin, copper, iron and silver were mined. There are few indications of metallurgical activity on an industrial scale; guess this was limited to the small foundries and local blacksmiths that produced the artifacts and equipment for daily use.

The catalyst for innovation and Roman construction significantly developed the manufacture of building materials, pottery and glass which were fired in kilns all over the territory, but few were intended for export, except perhaps from a few amphorae used for wine or oil. Likewise, the increase in population brought about a demand for better furniture and household accessories some of which were imported from other provinces of the Empire and paid for by income from mining and surplus agricultural products.

In recent times, a number of engineering studies have been undertaken in the Penamacor region in central Portugal to assess the profit that could be expected from a resumption of mining. This has piqued the interest of private prospectors who think ‘there is gold in these hills’, but it seems modern cost / performance ratios reduce feasibility, so hopefully local tranquility. , will not be disturbed.

Two videos are available on YouTube which give an excellent presentation of ancient mining practices. The first is from Speleo-TV and entitled “Mineração Romana em Valongo (Porto)” with English subtitles soon available while the second, produced in 2017, can be found on the Turismo de Três Minas website.

David C. Barham