Mértola lost 79% of its population since 1950 and rebuilt itself with what was buried

A port seventy kilometers from the sea

The tide still reaches Mértola. The Guadiana rises and falls twice a day next to the village's seawall, about 70 kilometers from the mouth, and it is this particularity — not the landscape, not the castle — that explains everything that happened there over the last two thousand years. Mértola is the southernmost point where a ship can reach. Above it, the river ceases to be used for transporting cargo.

That is why the Romans built a city there. Myrtilis received the Latin right from Octavian and the municipal status is believed to have been granted between 12 BC and 37 AD; Pliny the Elder includes it among the *oppida veteris Latii* and Ptolemy names it. It was not large: it occupied about five hectares, with a 1,291-meter wall and four identified gates. It was, rather, the place where the river and the road met.

The tension in this history lies in what happens when this advantage disappears. A city that exists because it is the end of navigation ceases to have a reason to exist when there is no longer navigation — and Mértola lost it twice, fifteen centuries apart.

What came down the river

From Myrtilis came the interior of Baixo Alentejo. Ore from the mines of Aljustrel and São Domingos, cereal from the surrounding *villae*, metals that archaeology identifies as silver, gold, and tin, shipped down the Guadiana to southern Hispania and the Mediterranean. In the opposite direction, wine and oil came up in amphorae — the so-called Greco-Italic and Dressel 1 found in the village are imports, not local production.

A port is measured by what appears in it that is not from there. In Mértola, coins from Emerita, Gades, Segóbriga, and Caesaraugusta appeared, as well as a gold coin of Nero with the legend CONCORDIA AVGVSTA. The epitaphs of Rossio do Carmo are in Latin, Greek, and with Hebrew symbolism; the Greek tombstones of the 6th and 7th centuries are the trace of Byzantine merchants in a village in the Alentejo interior.

These same funerary inscriptions give Mértola something few places have: documentary proof of continuity. The epigraphic work of Manuela Alves Dias makes it possible to attest uninterrupted occupation between at least the years 462 and 729 — crossing the end of Roman rule, the Visigothic period, and the arrival of the Arabs without any void.

Mîrtula, capital of itself

In 713, Mértola is taken by Musa ibn Nusayr, in the same movement that led to Medina Sidonia and Seville, and comes to be called Mārtulah. During Islamic rule, it is described as the westernmost port of the Mediterranean — which is another way of saying the same thing: it continued to be the navigable limit.

Twice it was the capital of its own State. The first taifa lasts from 1033 to 1044, founded by Ibn Tayfur, extending along both banks of the Guadiana, until it is absorbed by the taifa of Seville. The second is shorter and stranger: in the autumn of 1144, with the Almoravid power unraveling, Ibn Qasi — born in Silves, leader of the *murīdūn*, a Sufi movement of revolutionary contours — is proclaimed imam in Mértola. The imamate lasts until the summer of 1145. Ibn Qasi would later ally with the Almohads, govern Silves in their name, revolt with the support of Afonso Henriques, and end up decapitated by his own followers in 1151.

The Christian conquest arrives in 1238, by forces of D. Sancho II commanded by Paio Peres Correia. The following year the village is donated to the Order of Santiago; it receives a charter in 1254 and even becomes the seat of the chapter of the Order in Portugal, before the transfer to Palmela. The castle's keep, about 30 meters high, is completed in 1292.

The mosque that never stopped being used

The most improbable building in Mértola is the main church. It was built in the second half of the 12th century, during the Almohad period, as a mosque — and, unlike practically all others in the western Peninsula, it was not demolished to make way for a Christian temple. It was converted.

The floor plan can still be read. The original structure had six bays supported by twenty columns; the current one has four bays and twelve columns distributed across five naves. Four doors preserve horseshoe arches with *alfiz* framing. The minaret, with a square plan and about 15 meters, became the bell tower. The mihrab, on the southeast side, decorated with stucco forming three polylobed blind arches, was covered with plaster after the conversion and only exposed again much later.

Works in 1532 changed the roof, replaced the wooden ceilings with ribbed vaults, redistributed the naves, and added a Renaissance portal and Mudéjar-style merlons. It is this superposition — Almohad mosque, 16th-century adaptation, continuous religious use to this day — that makes the building a document and not a ruin. It is classified as a National Monument by decree of June 16, 1910, published in the Diário do Governo on June 23 of that year.

The century that gave everything and took everything

The river's second life begins in 1856, when the British firm Mason & Barry obtains the concession for the São Domingos mine, a little over twenty kilometers from the village. Extraction starts in 1858. The Romans had already been there — it is estimated that they removed about 150 thousand cubic meters of material, equivalent to 650 thousand tons —, but the industrial scale is different.

The numbers of the apogee explain the demographics of the entire municipality. The company once employed about 3,500 workers and the mining village reached 8,700 residents. In 1907, close to a thousand tons of ore were extracted per day; in 1914, about 400 thousand tons per year. Over 112 years of operation, more than 25 million tons of pyrite left from there.

To ship the ore, a railway of about 17 kilometers was built between the mine and Pomarão, on the Guadiana. It entered service in 1862 with animal traction and in 1867 switched to steam, with a 1,065-millimeter gauge — it was one of the first railway lines in the country, just two years after the Lisbon-Carregado line. The port of Pomarão was inaugurated in 1859; in 1864, 563 ships entered it. Mason & Barry continuously dredged the riverbed and maintained its own pilots to guide the boats. The mine installed the first power plant in Alentejo, and the complex featured a theater and a hospital.

In 1966, ore was extracted for the last time, with the deposit exhausted and prices down; in 1968 the company went bankrupt, with debts to the workers. What remained on the ground are about 25 million cubic meters of waste, of which close to 14 million are beneath the village, and an affected territory superior to six thousand hectares, with acid drainage that still darkens the water lines today.

The effect on the population is the most brutal data in this history. Mértola had 29,353 inhabitants in 1950, the maximum in its census series, and 26,026 in 1960. In 1970 it had 14,310 — 45 percent less in a single decade. The drop continued without interruption: 11,693 in 1981, 9,805 in 1991, 8,712 in 2001, 7,274 in 2011, 6,206 in 2021. Between 1950 and 2021 the municipality lost close to 79 percent of its inhabitants. Pomarão, the port through which millions of tons left, had 11 residents in 2023.

Less than five people per square kilometer

Mértola occupies 1,292.87 square kilometers — it is one of the largest municipalities in the country by area — and had 6,206 inhabitants in 2021. That is less than five people per square kilometer. Portugal had 112.2 inhabitants per square kilometer that year, and the European Union, in 2022, 109. Mértola has about one-twenty-third of the European average density.

The age pyramid tells the rest. In 2021, those under 15 years old were 8.8 percent of the population and those over 65 were 36.8 percent. In the sixties, young people were 27.9 percent and the elderly 8 percent — the two numbers practically swapped places in sixty years. In the most aged parishes of the municipality, the aging index exceeds one thousand elderly people for every hundred youths.

It is worth noting that this is not an isolated anomaly, and that is where the case ceases to be local. According to the 2021 Census, Portugal's 208 least dense municipalities concentrate about 20 percent of the population across 65.8 percent of the territory, while the seven most populous gather another 20 percent in 1.1 percent. On a European scale, Eurostat calculated that almost 60 percent of the one-square-kilometer cells in the Union and EFTA — 2.69 million cells — had no one living in them in the 2021 census.

What was done with what was left underneath

In 1978, twelve years after the mine's closure and with the municipality in the middle of its demographic decline, the Mértola Archaeological Field was founded, largely on the initiative of archaeologist Cláudio Torres. It was not a museum: it was a non-profit association that excavated and, as it excavated, opened museum nuclei within the village itself, rather than concentrating everything in a single building. The first nuclei were set up between 1991 and 2001 — the castle, the paleochristian basilica, the weaving workshop, the blacksmith's forge, sacred art, Islamic art. Today the Mértola Museum – Cláudio Torres brings together fourteen units and the museum-village tour has sixteen stops, including the São Domingos mine and Alcaria dos Javazes.

The model was recognized early on: National Award for Nature Conservation and Historical-Cultural Heritage in 1989 and Cultural Merit Medal from the Ministry of Culture in 1998. And it had a measurable effect. Between 2012 and 2017, entries to the main church rose from 26,617 to 46,426, and those to the alcazaba from 5,837 to 29,126 — a fivefold increase. The Islamic Festival, biannual since 2001, expected 60 thousand visitors in the 2023 edition: about ten people for each resident of the municipality, in a single weekend.

The closest European comparison is Bruges. The Zwin canal, opened by a storm in 1134, made the city one of Europe's largest medieval ports; silting began in the late 13th century, and by around 1500 the canal was unusable. Bruges became impoverished, stopped rebuilding — and it was precisely this standstill that preserved the medieval fabric that sustains it today. Mértola takes the reverse path: in Bruges, what remained in sight became the asset; here the asset was buried and had to be unearthed by those who decided to stay.

A piece is missing, and it is the initial one. The navigability of the Guadiana is being restored in phases with European funds: Vila Real de Santo António–Alcoutim and Alcoutim–Pomarão are completed; the third phase, Pomarão–Mértola, plans a channel at least 30 meters wide and two meters of service depth, for vessels up to 70 meters. If completed, the river will return to the place where it always stopped — and it is the first time in sixty years that this is being considered.