Scattered across the landscapes of Ireland, Great Britain, parts of Scandinavia, and northern Europe are enigmatic fortified structures known as ringforts. These circular or oval enclosures, bounded by earth walls and ditches, mostly date from between 500 and 900 AD, a period that spans the late Bronze Age to the early Middle Ages in these regions.

They are particularly abundant in Ireland, with over 40,000 sites identified to date, averaging one site per every 2 square kilometers. Many have likely been destroyed by modern agriculture and construction, but new ones continue to be discovered through archaeological surveys.

In the Irish language, they have different names such as rath, lios, caiseal, cathair, and dún. Rath and lios refer to earth forts, while caiseal and cathair are used for stone forts. Dún was used to designate any fortress. Similar sites in Cornwall and Wales are called rounds.

Ringfort in County Kerry, Cahergall Cashel
Ringfort in County Kerry, Cahergall Cashel. Credit: Leprechauan / Wikimedia Commons

In Scandinavia, only the Swedish island of Öland has 19 of these structures, which are different from the later Viking ring fortresses of the late 10th century AD.

Ringforts vary greatly in size, generally from 15 to 50 meters in width. The earth ones have circular walls of earth or stone surrounding an open central space. The wall may also be made of wood with stones and earth added. Some sites are surrounded by multiple concentric rings of banks and ditches.

Inside, there is always at least one building, either round or rectangular, used for housing or storage. Some forts also have underground tunnels. The walls are typically 2-3 meters high and 5-10 meters wide at the base.

Interior of the ringfort of Grianán of Aileach in Donegal, Ireland
Interior of the ringfort of Grianán of Aileach in Donegal, Ireland. Credit: Gareth Wray / Wikimedia Commons

On rare occasions, some enormous ringforts served as significant meeting and ceremonial assembly points in the later Early Middle Ages. The Hill of Tara, the ancient inauguration site and seat of the High Kings of Ireland, may have originated as a type of giant ringfort.

The main debate about these ring forts is when most of them were built and occupied. Some argue their origin dates back to the Iron Age, based on similarities with the hillforts of Great Britain and the Iberian Peninsula. However, most experts agree that the majority date from between 500 and 900 AD.

Radiocarbon dating shows that more than 50% of the excavated ones date from 540-884 AD, and two-thirds from 600-900 AD. The concentration of ringfort construction in this period coincided with the dominance of Gaelic kingdoms and a growing cattle-based economy.

Ringfort at Rathrá, Co Roscommon, Ireland
Ringfort at Rathrá, Co Roscommon, Ireland. Credit: West Lothian Archaeological Trust (Jim Knowles, Frank Scott and John Wells) / Wikimedia Commons

Although their function has long been debated, most archaeologists today believe each ringfort was likely the farmstead of each free member of a clan. That is, an enclosure where agricultural and craft activities were carried out, and at the same time served as a fortified dwelling.

Not all forts show signs of full-time settlements. Some may have been industrial centers, livestock enclosures, or aristocratic sites.

The circular walls and ditches appear defensive, but contemporary texts associate them more with nobility and status. Kings inhabited elaborate forts with multiple embankments as symbols of authority. With their circular shape and watch posts, ring forts offered some protection in case of attack on livestock. It is possible that groups of ringforts scattered across the countryside acted as mutual watch points.

Another view of the ringfort of Grianán of Aileach
Another view of the ringfort of Grianán of Aileach. Credit: Mark McGaughey / Wikimedia Commons

Ringforts declined in Ireland after 900 AD but evolved into motte-and-bailey castles under the Normans by building wooden towers on top.

According to Gerald of Wales, by 1200 AD, ringforts had largely been abandoned. The memory of their original function was lost, but their earthworks remained prominent landscape features, associated until recent times with places where fairies and giants lived in popular folklore. Some ringforts, like Kelly Rounds in Cornwall, are linked to the legend of King Arthur.

One of the most famous ringforts outside the British Isles is Sandby Borg on the Swedish island of Öland, where a terrible massacre occurred in the 5th century AD, still unexplained.

More than a thousand years later, ringforts still dot the Irish countryside, though covered in vegetation. Other places where they can be seen, albeit in much smaller numbers, include Wales, Cornwall, Denmark, Sweden, Germany, and Estonia.

This article was first published on our Spanish Edition on October 18, 2023: Los enigmáticos fuertes anulares de Irlanda y Gran Bretaña, donde viven las hadas y los gigantes de las leyendas

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