Fortified Sites in Celtic Britain

Even though hill-forts and brochs are the most frequently occurring Celtic fortifications in Britain, there were other types of fortified sites that coexisted with them. However, this article will not examine the less defensible sites like lake villages and crannogs due to their lack of apparent means of defence, aside from being surrounded by water. The lake village at Glastonbury in Somerset, for instance, had a wooden palisade around it, but it was likely constructed to prevent children and animals from falling into the adjacent lake rather than to repel invaders. Similarly, structures built over water, such as the Oakbank Crannog in Scotland’s Loch Tay, may have been defensible for a short time but were insufficient to withstand determined attackers. Therefore, this study will focus on the Celtic sites that were apparently designed with defence as a primary consideration.

Why were hillforts built?

Strategically located on higher ground, these settlements provided a natural defence against rival tribes. Hillforts were able to accommodate a large number of people, often hundreds at a time, making them crucial for protecting the tribe’s interests. As a result, they were a prevalent type of settlement during this period, serving as an important part of the social and cultural landscape of the time.

Types of Hillfort and Celtic defensive structures

Celtic fortifications exhibit various types, though most share similar features, except for brochs. To classify the intricate systems of ditches and banks found, archaeologists have developed terminology that utilizes familiar fortification terms. For instance, the words “bank” and “rampart” are frequently used interchangeably, but the latter should specifically apply to the innermost bank encircling the fort’s enclosure. If a fort is enclosed by a single circuit of bank and ditch, it is called a “univallate” fort. More intricate fortifications are labelled “bivallate” if they have two lines of defence, “trivallate” if they have three circuits of bank and ditch, and “multivallate” if they have more than three lines of defence. Banks that are placed closely together are termed “compact,” while those spaced apart are considered “dispersed.”


The first type of Celtic fortifications are the pure hill-forts, whose defences are strategically positioned to take advantage of the terrain. The fort’s perimeter follows the contours of the hilltop it is constructed on, causing these fortifications to be seldom circular or symmetrical. Instead, the lines conform to the hill’s shape, resulting in an irregularly shaped but tactically advantageous defensive position. A variation of this type is the headland or promontory fort, situated on rocky spurs of coastlines where the location can be made defensible with minimal effort.

Promontory Fort

Another variation of Celtic fortifications is the headland or promontory fort, which can be found on rocky spurs along coastlines. These sites are easily defensible with minimal effort. Examples of such fortifications can be found at Burghead in Moray, Scotland, and Rame Head in Cornwall. They use a defensive system of banks and ditches similar to that of hill-forts to close off the landward side of the headland. The only difference is that the sea serves as a natural barrier on the remaining sides of the fortified position. It is important to note that promontory forts are not always found on the coast. The Iron Age settlement at Dyke Hills in Oxfordshire is a perfect example of establishing a similar position that provides an advantage, far from the sea. This settlement was strategically located at the confluence of two large rivers, namely the River Thame and the River Thames, near modern-day Dorchester-on-Thames. To protect the settlement, a bivallate defensive line was created, while the two rivers served as a natural defense mechanism for the remaining three sides of the site. Such locations with natural barriers provided an excellent opportunity to build a fortified settlement that could withstand potential attacks.

Plateau Fort or Valley Fort

The plateau fort or valley fort is a variation of the hill-fort, lacking defensive advantages such as slopes or rivers. Instead, these relied on man-made defences to keep attackers at bay. The only advantage was that the fortification often included a natural spring, providing access to water and better chances of withstanding a siege. These forts were usually built in areas of good farmland, on broad ridges, or in valleys where no more defensible feature was available. For instance, Rainsborough in Northamptonshire is an early Iron Age fortification that stood on the edge of a plateau, enclosing an area of 2.5 hectares. Its defences were univallate, and traces of an outer bank were found during excavation. However, the gateway was destroyed by fire, and a skeleton was discovered amid the burned ruins of a guardhouse, indicating that the fort was attacked and captured, probably in the 3rd century BC.

Non-defensive enclosures

A unique group of forts exists that were constructed as non-defensive enclosures, most likely for housing livestock or providing a seasonal residence for a farming community. These sites were often erected on hillsides or flat terrain and involved multiple enclosures surrounding a central area. Though these were not primarily built as defensive positions, they could serve as emergency refuges during times of danger. Examples of such forts include Lordenshaws in Northumberland and Clovelly Dykes in Devon, typically found in the north of England, the south-west, or the western coastal fringe of Wales. At Clovelly Dykes, a central compound of 1.2 hectares was surrounded by an oval bank and ditch, which was then encircled by another full bank and ditch, plus two low-banked enclosures, some of which had associated ditches. The site also had a large annex enclosure on its western side, safeguarded by another ditch. In total, the fortification covered an area of around 9.6 hectares. The complex site was expanded during its occupancy, with outer enclosures added after the innermost enclosure was built. The minor nature of the outer works suggests that they served as livestock enclosures, while the inner enclosure housed a small farming community or even a large farmstead.

Ring Forts

In Scotland, smaller fortified enclosures called ring forts or raths have been discovered. These enclosures were usually univallate and had a circular or near-circular bank and ditch system for protection. Some enclosures were built on level ground, while others encompassed natural or artificial mounds. The ring forts in Glen Lyon may have been constructed as boundary markers or outposts to protect the Iron Age community of Loch Tay and the summer pastures in the hills. Some ring works protected farmhouses, similar to fortified farmhouses in medieval Europe. Dan-y-Coed and Woodside in Dyfed, Wales, were both strongly fortified with a bivallate defensive system and approached along a pathway lined by more banks. These were likely farming settlements rather than villages, as archaeological evidence showed roundhouses without central hearths, indicating the presence of farm buildings instead of dwellings.


The majestic brochs, towering stone structures located in northern Scotland, may have some similarities with the stone-clad ring forts in central Scotland or the stone-built hill-forts in Wales. However, there is little evidence to suggest that the builders of these structures were associated with those of Celtic sites in other parts of Britain.