‘Give us this day our daily bread’: how grain silos improved food security in ancient times

​The sixth line from the Lord’s Prayer asks God to provide us with the essentials that keep body and soul together. Long before those words were written, our distant ancestors took more practical steps to reduce the risk of dying of starvation in troubled times. A key part of their survival strategy was the silo.

​With the world in its current state, the word ‘silo’ will make some people think of a deep pit from where long distance missiles – nuclear or otherwise – may be launched. A more peaceful sight are the shiny metal silos I can see from my home, above ground and full of grain harvested from the surrounding fields.

The original meaning of the word ‘silo’ lies somewhere between the two: a storage pit in the ground rather than above it, but used to store grain rather than missiles. 

​In his ‘Naturalis Historia’ written during the 1st century CE, Pliny the Elder devotes a whole chapter to methods of storing corn. He lists several options including brick granaries with walls three feet thick, no windows allowed, or wooden granaries on pillars. But the best way of preserving grain, he assures us, is to store it in trenches called ‘siri’, a practice that was common in Cappadocia, Thracia and Spain. Over the following centuries, ‘siri’ mutated into silo in Spanish or perhaps zilo in Basque and then entered the English language in the 19th century.

​Pliny’s instructions for building a silo are simple: dig a hole in dry soil, place a layer of chaff at the bottom and fill it up with grain still on the ear. He claims that noxious insects will never breed in grain stored in this way, and that wheat will keep for up to fifty years and millet a hundred!

​Even the learned Pliny would not have guessed that this practice was already several thousand years old at the time he was writing, even in and around the Pyrenees. Excavations carried out inside a cave in the Spanish Pyrenees between 2011 and 2013 (Coro Trasito) found silos which had been used to store grain around 7,000 years ago. That is roughly the time when the first migrants introduced farming to this part of Europe.

​Between the 6th and 5th centuries BCE – still long before Pliny – agricultural output in this region had increased so much that Iberian tribes on both sides of the Pyrenees constructed fields of underground silos to store reserves of grain. In recent years, over a thousand of these storage pits have been excavated by archaeologists in the area between Girona and Perpignan, and at more elevated sites in the mountains in between. Their capacities range from around 300 to 8,500 litres.  To appreciate the effect this would have had on food security, each silo would have contained enough grain to bake between 800 and 20,000 modern baguettes.

​One particularly intriguing site is a city built between the 4th and 3rd centuries BCE by a tribe called the Cerretani in what is now the Spanish half of the Cerdagne. Archaeological excavations began in 2006, but once half-a-dozen silos had been explored, they were filled in again. Although this was a sensible safety measure, it rather spoils the visual impact. Fortunately, a town much closer to my own home in the south of France has an abundance of silos which are easier to examine. 

​Lautrec stands on a hill between Castres and Albi. As well as the defensive advantages of altitude, geology undoubtedly played a role in the selection of this site in ancient times. The hill is made of dense sandstone, perfect for hollowing out silos. Even better, water is forced up through fault lines in this rock. As a result, nearly every house in Lautrec has a water well and at least one silo in its cellar. In total, around 160 silos have now been identified, and some of them may date back to Gallo-Roman times. In 2011, 28 silos were discovered in the cellar below a single building – the Maison Leblanc. When  these silos were full, each one would have held between 1 tonne and 2.5 tonnes of wheat, maize or lentils.

Various theories of exactly how this type of storage system worked have been proposed over the years. According to INRAP, France’s national institute for preventive archaeological research, grain was cleaned and dried before being poured into a silo which was then hermetically sealed. After a few days, the layer of grain in contact with residual humidity in the silo’s walls would have germinated and consumed all the oxygen trapped inside the silo. The oxygen-free air was then ideally suited to the conservation of the bulk of the grain, keeping it in a dormant state. When the silo was opened one or several years later, the grain could have been used to sow a new crop, trade for other goods or ground into flour to give people their daily bread.

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