A hillfort is a strong, protected place built on high ground to help people stay safe. These structures were common during the late Bronze Age and Iron Age in Europe. Some hillforts were used after the Roman Empire ended. The walls of a hillfort usually follow the shape of a hill and include earth or stone barriers, wooden fences, and ditches around the outside. If enemies came near, people living in the hillfort could see them from far away.
In ancient Europe, the number of people living there grew over time. Around 5000 BC, during the Neolithic period, about 2 to 5 million people lived in Europe. By the Late Iron Age, the population had grown to about 15 to 30 million. Outside of Greece and Italy, most Iron Age settlements were very small, with only about 50 people living in each. Hillforts were different because they could hold up to 1,000 people. Later, during the Late Iron Age, larger settlements called oppida appeared, with as many as 10,000 people living in them. As the population increased, societies became more complex. Hillforts first appeared around 1100 BC and spread across Europe. These places had many uses, including serving as tribal meeting spots, safe places during attacks, areas for religious ceremonies, and centers for making tools or goods.
Hillforts were sometimes used by armies that conquered other lands. However, in other cases, the forts were destroyed, and the people living there were forced to leave. For example, Solsbury Hill was attacked and abandoned during the Belgic invasions of southern Britain in the 1st century BC. Some abandoned forts were later used again when new threats appeared, such as during the Dukes' Wars in Lithuania and during later invasions of Britain by the Romans, Saxons, and Vikings.
Celtic hillforts
Celtic hillforts began during the Late Bronze and Early Iron Age, around the start of the first millennium BC. They were used in many Celtic areas in central and western Europe until the Romans conquered those regions. They were most common during later periods.
The Hallstatt culture and La Tène culture originated in what is now southern Germany, Switzerland, Austria, Slovakia, and the Czech Republic. The main way to build ramparts was called pfostenschlitzmauer, or Kelheim-style. During the Hallstatt C period, hillforts became the main type of settlement in western Hungary. Julius Caesar called the large Late Iron Age hillforts he saw in Gaul oppida. By this time, larger hillforts resembled cities more than fortresses, and many became Roman towns.
The reasons for the rise of hillforts in Britain and their purpose have been debated. Some believe they were built in response to invasions from Europe, by invaders, or to manage social tensions caused by growing populations and pressure on farming. Since the 1960s, the most accepted view is that the use of iron changed society in Britain. Iron ore was found in different places than tin and copper, which were needed for bronze. This changed trade patterns and weakened old elites. Power shifted to new groups. Archaeologist Barry Cunliffe believes population growth also played a role. He said hillforts provided defense during times of conflict but were not necessarily built because of constant war. Some were attacked, but this was not the main reason for their construction.
Hillforts in Britain date back to the Bronze Age, but the most active period of building them was during the Celtic Iron Age, between 700 BC and the Roman conquest of Britain in 43 AD. The Romans occupied some forts, such as the military garrison at Hod Hill and the temple at Brean Down. Others were destroyed or abandoned. At Cadbury Castle, remains of 28 to 40 people were found, which some believed linked to a revolt in the 70s AD, around the same time as Boudicca’s rebellion. However, later researchers questioned this. Barracks on the hilltop after the Roman conquest suggest local resistance continued.
Maiden Castle in Dorset is the largest hillfort in England. In areas with less Roman influence, such as uninvaded Ireland and northern Scotland, hillforts were still used for many years.
There are over 2,000 Iron Age hillforts in Britain, with nearly 600 in Wales. Danebury in Hampshire is the most studied and published Iron Age hillfort in Britain. Cadbury Castle in Somerset was reoccupied after the Romans left to defend against pirates and Anglo-Saxon invasions. A cemetery near Poundbury Hill has Christian burials from the 4th century CE. In Wales, Dinas Powys was a Late Iron Age hillfort reused from the 5th–6th centuries CE. Similarly, Castell Dinas Brân, a hillfort from around 600 BCE, was reused in the Middle Ages, with a stone castle built there in the 13th century CE.
Some Iron Age hillforts were used in medieval frontier defenses. For example, Offa’s Dyke, a 9th-century CE earthwork, used parts of the Llanymynech hillfort. The hillfort at Old Oswestry was included in Wat’s Dyke, an early medieval earthwork. The Wansdyke connected to Maes Knoll hillfort, marking the Celtic-Saxon border in southwest England between 577–652 CE.
Some hillforts were reused by the Anglo-Saxons during Viking raids. King Alfred built a network of coastal hillforts and lookout posts in Wessex, connected by military roads to track Viking movements. Examples include Daw’s Castle and the Battle of Cynwit.
It has been suggested that some hillforts were used to enclose animals like cattle and horses. Large examples at Bindon Hill and Bathampton Down covered more than 50 acres. Even Iron Age hillforts used for defense were sometimes repurposed for corralling animals later. Examples include Coney’s Castle, Dolebury Warren, and Pilsdon Pen. However, it is hard to prove whether people lived there, as the lack of evidence does not confirm absence.
Bronze Age and Iron Age hillforts are common in Ireland, with over 500 identified in Ireland and Northern Ireland. These are large circular structures, usually 1–40 acres in size, enclosed by stone walls or earthen ramparts. They were likely tribal centers where leaders lived with their families and farmed or rented cattle to others.
About 12 of these hillforts are multivallate, meaning they have multiple ramparts or a large outer bank. The hillfort at Mooghaun is an example, defended by multiple stone walls.
It is important to distinguish hillforts from medieval ringforts, which are common in Ireland. Over 40,000 ringforts have been found, and some may still be undiscovered.
Other hillforts in Europe
In Galicia, Asturias, Cantabria, the Basque Country, the province of Ávila, and Northern Portugal, a castro is a type of fortified village from the pre-Roman Iron Age. These villages were usually built on hills or other naturally defensible areas. Larger hillforts were sometimes called citanias, cividades, or cidás, which means "cities" in English. These hillforts were located on hilltops, which helped control the surrounding area and provided natural protection. They often had access to a spring or small stream for water, and some had large reservoirs to use during sieges. A castro typically had one to five walls made of stone and earth, which worked with the natural defenses of the hill. The buildings inside were mostly circular, though some were rectangular, and ranged in size from about 3.5 to 15 meters long. They were made of stone, with thatched roofs supported by wooden columns in the center. In larger settlements, there were regular streets, showing some level of organization. Castros varied in size from less than one hectare to as large as 50 hectares, and most were abandoned after the Romans conquered the region.
Many castros were built during the Atlantic Bronze Age, which was before the Hallstatt culture.
Many large stone structures from the Bronze Age, such as menhirs and dolmens, which are often found near castros, were built before the arrival of the Celts in Portugal, Asturias, Galicia, and other regions like Atlantic France, Britain, and Ireland. These structures may have been used in rituals by Celtic Druids.
The Celtiberian people lived in an inland area of central northern Spain, near the upper valleys of the Ebro, Douro, and Tajo rivers. They built hillforts, fortified hilltop towns, and oppida, including Numantia.
During the Migration Period (300–600 CE), many hilltop settlements were built on both Roman lands and areas controlled by Germanic peoples. However, these settlements varied greatly in size and purpose. Some Germanic settlements had fortifications, but unlike the Romans, they did not use mortar in their construction. Notable hill settlements in Germany include Runder Berg near Bad Urach and Gelbe Burg near Dittenheim.
In Sweden, hillforts from the Iron Age were used for various purposes. They were often built on hill crests, using steep slopes and marshes as natural defenses. Walls of stone and outer walls on the slopes were common. Round, enclosed forts called ring forts were also found on flat ground. The walls sometimes had remains of stone that supported wooden fences. Many hillforts had clearly marked gateways, likely made of wood. Some hillforts with strong walls were near old trade routes and had an offensive purpose, while others were smaller and used for hiding during attacks.
Many forts in densely populated areas were permanently occupied and show signs of both inside and outside settlements. Old place names with the words "sten" or "stein" often referred to hillforts.
In Sweden, there are about 1,100 known hillforts, with the highest concentration on the northern west coast and in eastern Svealand. There are 300 in Södermanland, 150 in Uppland, 130 in Östergötland, and 90 to 100 each in Bohuslän and Gotland. Norway has about 400 hillforts, and Denmark has 26.
In Finland, the word for hillfort is "linnavuori" (plural: "linnavuoret"), meaning "fort hill" or "castle hill," or "muinaislinna," meaning "ancient fort." Unlike later forts, many Finnish hillforts were once located near the sea, though many are now farther inland due to changes in land levels after the last ice age. Finland has about 100 confirmed hillforts and 200 more suspected sites. The largest is Rapola Castle, with other notable examples including the Old Castle of Lieto and the Sulkava hillfort.
In Estonia, the word for hillfort is "linnamägi" (plural: "linnamäed"), meaning "hillfort" or "hillburgh." There are hundreds of hillforts or suspected ancient sites across Estonia. Some, like Toompea in Tallinn or Toomemägi in Tartu, have been used as centers of governance from ancient times to the present. Others, like Varbola, are historical sites. Estonian hillforts were likely used as administrative, economic, and military centers by tribes before Christianity. Some were only used during times of danger and stood empty during peace. A list of Estonian fortresses includes castles, fortresses, forts, and hillforts.
In Latvia, the word for hillfort is "pilskalns" (plural: "pilskalni"), from "pils" (castle) and "kalns" (hill). Hillforts in Latvia served military, administrative, cultural, and economic purposes. They were often part of larger complexes that included settlements, burial sites, and ritual areas. The first hillforts in Latvia, like Daugmale, appeared during the Bronze Age. Some were inhabited until the late Iron Age. During the Roman Iron Age, some hillforts, like Ķivutkalns, were abandoned or became sparsely populated. A new wave of hillforts developed between the 5th and 8th centuries AD, often near rivers. By the 10th–11th centuries, some hillforts became strong military fortresses, such as those in Tērvete, Talsi, and Mežotne. These sites were important political centers during a time of social and political changes. Most Latvian hillforts were destroyed or abandoned during the Livonian Crusade in the 13th century, though some were used into the 14th century. Latvia has about 470 hillforts.
In Lithuania, the word for hillfort is "piliakalnis" (plural: "piliakalniai"), from "pilis" (castle) and "kalnas" (mountain or hill). Hillforts in Lithuania date back to the Bronze Age, with the earliest examples found in the eastern part of the country. Most were built or expanded between the 5th and 15th centuries, used during conflicts like the Dukes' Wars and against the Teutonic Knights. These fortifications were usually wooden, though some had stone or brick walls. The hills were often shaped for defense, with the top flattened and slopes made steeper. During the early years of the Grand Duchy of Lithuania, hillforts played a major role in conflicts with the Livonian Order and Teutonic Knights. Two main defense lines were established:
Hillforts elsewhere in the world
Similar structures are found in other places around the world, such as the Hill Forts of Rajasthan.
In the Philippines, the Ivatan people of the Batanes Islands built ijang—fortified villages on top of natural hills and raised landforms near coastlines. These villages were built with terraces that formed defensive walls, and had few places to enter. Artifacts found in an ijang in the town of Savidug on Sabtang Island date back to about 1200 CE. These high rocky areas were used as safe places to escape from enemies. The English explorer Captain William Dampier first described ijang in 1687 during his visit to the island of Ivuhos. During the Spanish colonial period, ijang were abandoned when the Ivatan people were moved to centralized towns in the lowlands as part of the Reducciones.
Among the Māori people, villages called pā were often built on raised ground, such as volcanic hills, headlands, and small islands, including man-made islands. The slopes of these locations were built into terraces that formed defensive walls, which were often protected by wooden fences. Traditional pā had many different designs, ranging from simple terraced hills to complex structures with multiple rows of fences and underground defensive areas. Māori pā differed from European hillforts because they also included food storage pits and water sources. These villages lasted until the colonial era. Later versions of pā were designed specifically for fighting with guns.