Coastal Defences & the Saxon Shore

By the time of Antoninus Pius, the boundaries of the Roman Empire had largely stabilised, aside from modest expansions under Marcus Aurelius. Subsequent efforts focused less on expansion and more on refining the empire’s frontier defences. Enhancements were made to improve the efficiency of border patrols and to respond to emerging threats. One such response was the establishment of a third-century coastal defence system in Britain and northern Gaul—commonly known as the “forts of the Saxon Shore.”

These forts, built at key estuaries and inlets along the Channel coast, are recorded in the late Roman document Notitia Dignitatum, which places them under the command of the Count of the Saxon Shore. This reference has led to the widespread belief that they were manned by Roman troops defending against seaborne Saxon raiders. Many of these forts still survive in some form today, and the name endures in the 153-mile Saxon Shore Way.

However, while they illustrate a unique Roman response to maritime threats, the Saxon Shore forts represent a different kind of frontier—more fragmented and reactive—than the structured overland and riverine limes of the continental empire. As such, this coastal system, though noteworthy, falls outside the primary scope of this work’s analysis of Rome’s more formalised frontier infrastructure.

The Forts of the Saxon Shore

Nine forts along the east and south-east coasts of England are listed in the Notitia Dignitatum as being under the command of the Count of the Saxon Shore. These can be identified with surviving Roman remains stretching from the Wash in Norfolk to the Solent in Hampshire. Each was strategically positioned to guard key estuaries and sea routes.

Brancaster (Branodunum), Norfolk guarded the approach to the Wash. Though now mostly buried, the fort’s layout—covering 2.6 hectares in the typical “playing card” shape—can still be discerned through aerial photographs showing the lines of its ramparts, gates, and internal structures. An external civilian settlement is also visible.

Burgh Castle (Gariannonum), Norfolk stands on a hill overlooking the river Waveney. Once coastal, it now lies inland due to changes in the landscape. The fort, enclosing 2.4 hectares, retains three of its thick stone walls, up to 4.5 metres high in places, with six projecting towers possibly added in a later phase.

Bradwell-on-Sea (Othona), Essex was positioned to monitor the Blackwater and Colne estuaries leading to Camulodunum (Colchester). Although little survives above ground, the 7th-century chapel of St Peter-on-the-Wall now stands over the Roman west gate, reusing building materials from the fort.

Reculver (Regulbium), Kent guarded the northern end of the Wantsum Channel, once separating the Isle of Thanet from the mainland. The fort, roughly 180 by 175 metres, retains parts of its walls and is partially overlain by the ruined church of St Mary. Erosion has claimed nearly half of the site.

Richborough (Rutupiae), Kent is widely considered the landing site of the Roman invasion in AD 43. Initially a military base and later a port town, it saw successive fortifications in the 3rd century. The site preserves triple ditches from an early fort and striking stone walls from a later one dated to around AD 275–285.

Dover (Dubris), Kent was originally the site of a fleet base (classis Britannica) established shortly after the conquest. The first fort, begun around AD 117, was abandoned in the early 3rd century. A second fort was built around AD 270, though much of it is now hidden beneath modern development.

Lympne (Portus Lemanis), Kent lies on the edge of Romney Marsh, now inland due to silting. The fort, covering 3.4 hectares in an irregular pentagon, suffers from unstable ground, causing walls—up to 6 metres high—to lean or collapse in places.

Pevensey (Anderida), East Sussex features a large oval enclosure with innovative D-shaped towers, typical of late 3rd-century Roman military architecture. Enclosing 4 hectares, its walls were later incorporated into a medieval castle’s outer bailey.

Portchester (Portus Adurni), Hampshire is the best-preserved Roman fort north of the Alps. Its walls form a square with 20 D-shaped bastions, 14 of which survive. Much of the circuit remains intact, though altered in parts by a 12th-century medieval castle.

Additional Shore Forts in Roman Britain

In addition to these nine forts, two further sites on England’s east coast may also have played a role in this coastal defence network:

Caister Roman Site, Norfolk guarded a now-silted estuary. Though overbuilt by modern housing, parts of the wall and ditch remain, along with foundations of internal buildings. The fort covered nearly 3.5 hectares.

Walton Castle has largely been lost to coastal erosion, but early drawings show a design similar to Burgh Castle. It has occasionally been confused with Portus Adurni, now more securely identified as Portchester.

Additional Shore Forts in Belgium and Netherlands

The Notitia also mentions two Saxon Shore forts on the Continent: Oudenburg in modern Belgium and Aardenburg in the Netherlands, indicating that this system of maritime defences extended across the Channel to protect the Roman provinces of Germania Inferior and Gallia Belgica.

The Notitia Dignitatum

The Notitia Dignitatum – meaning “List of Offices” – is a late Roman document that records the senior administrative and military roles across the Empire, along with their jurisdictions. It’s divided into two main sections: one detailing the eastern empire, which reflects the state of affairs around AD 395, and another covering the west, including Britain.

The western section appears to be a compilation drawn from multiple sources of varying dates. Some entries were likely outdated by the time they were included, and portions of the text are missing altogether. Scholars generally date its final compilation to between AD 390 and 420, though parts may be based on older material.

Among its listings is a high-ranking official titled Comes litoris Saxonici per Britanniam – the Count of the Saxon Shore in Britain – alongside a roster of forts and garrison units under his command. However, it’s unclear when this position was created or how long it had existed before the Notitia was written.

The reason for the term “Saxon Shore” is also uncertain. The most widely accepted explanation is that it referred to a stretch of coastline vulnerable to seaborne raids by ‘Saxons’—a name Roman writers used broadly for Germanic groups such as the Saxons, Franks, and Frisians who lived along the North Sea coast, in present-day northern Germany, Denmark, and the Netherlands. A less likely theory suggests that it denoted areas where Saxon settlers had been permitted to reside under Roman rule.

Click Here for further details on the Notitia Dignitatum

The Early 3rd-century forts

During the AD 230s, three Roman forts were constructed along the eastern coast of Britain—at Brancaster and Caister-on-Sea in Norfolk, and Reculver in Kent. Around the same period, two existing forts across the Channel, at Oudenburg and Aardenburg, were reconstructed. These continental forts likely originated in response to raids by Germanic seaborne attackers, a threat mentioned in Roman sources from the later 2nd century AD. Archaeological evidence supports the establishment and rebuilding of fortifications along these coastal zones during this time.

A reconstructed inscription found in the principia (headquarters building) at Reculver suggests the fort’s construction took place in the 230s. The inscription names a figure called Rufinus, who may be Q. Aradius Rufinus—a Roman official who later held high-ranking posts in Africa in AD 238.

RIB 3027 - Fragmentary building inscription

• Translation
• Latin
• Commentary

The forts at Brancaster, Caister, and Reculver all feature the typical Roman “playing card” layout: rectangular plans with rounded corners, enclosed by stone walls and backed with substantial internal earth ramparts. Their design echoes the style of earlier Roman forts from the 1st and 2nd centuries AD. Gateway structures vary: Reculver had two single-portal gates, Caister featured a double-portal south gate, and Brancaster may have also had a double-portal gate.

Internally, Reculver followed conventional Roman military design, with structures such as barracks, a headquarters building, and the commandant’s residence. At Caister, only a portion of a courtyard building has been excavated—possibly the commanding officer’s house, later repurposed as a workshop. Brancaster’s interior shows some deviation from the standard grid plan: one building lies at a different angle, possibly a mansio (a government-run guesthouse and relay station). Uniquely, Brancaster also included a training arena for cavalry horses—an uncommon feature in Roman Britain.

Some scholars argue that these newly built British forts, alongside the rebuilt continental ones, represent the earliest organized system of cross-Channel defences against maritime raiders. However, there is no direct documentary evidence of raids in Britain during this period, and although two of these forts are later listed in the Notitia Dignitatum, they were constructed more than 160 years before that document was compiled.

The Late 3rd Century Forts

During the latter part of the 3rd century AD, a new wave of fort-building took place along Britain’s east and south-east coasts. Notable examples from this period—many with substantial remains still visible—include Burgh Castle (Norfolk), Bradwell-on-Sea (Essex), Richborough, Dover and Lympne (Kent), as well as Pevensey (East Sussex) and Portchester (Hampshire). These, together with the earlier forts of the 230s, form the complete roster of installations recorded in the Notitia Dignitatum. One additional fort, known historically as Walton Castle, was similar in design but was never listed in the Notitia and has since been lost to coastal erosion.

In contrast to the regular layouts of earlier 3rd-century forts like Brancaster, Caister and Reculver, these later forts adopt a more varied and irregular approach to design. This shift likely reflects significant changes in military doctrine and administrative structure. The forts range in shape from Burgh Castle’s elongated rectangle and Portchester’s near-perfect square to Lympne’s asymmetrical polygon and Pevensey’s elongated oval.

These later forts are characterised by their formidable masonry. Most had thick stone walls—up to 4 metres wide and in some places 8 metres high. Unlike their predecessors, many of these did not rely on internal earth ramparts, though Dover and Bradwell are exceptions. One of the key innovations in this period is the systematic use of projecting towers, both rectangular and rounded, spaced along the perimeter walls and at the corners. These allowed defenders to fire laterally along the fortifications, greatly enhancing their defensive capability.

Gates also underwent a redesign. Unlike the multi-portal entries of earlier forts, these later forts generally featured fewer gates, most of which had a single entranceway. The gates at Portchester and Pevensey were especially well fortified—set back from the main wall line to create a confined space that could be defended from three directions, a tactic designed to trap and neutralise attackers.

Although the interiors of these forts remain poorly understood, and few stone structures have survived, some notable features have been uncovered. Bath-houses were identified at Dover and Richborough, and evidence from Portchester reveals the presence of families—women and children living alongside soldiers—within the fort walls.

Archaeological research suggests that these coastal forts were constructed between approximately AD 260 and AD 300. Portchester and Pevensey can be dated more precisely, to around AD 286 and AD 293 respectively. In some instances, new fortifications were built over earlier ones—for example, at Dover, where an earlier fort dating back to around AD 130 had been abandoned by AD 225. At Richborough, a small triple-ditched enclosure built around AD 250 was replaced by a substantial stone fort between AD 275 and AD 290.

Why were these Forts Built?

By the middle of the 3rd century AD, Roman sources report frequent raids along the continental coast of the Channel by Germanic groups. While many of these incursions were relatively minor, there were also major invasions—most notably those that pushed deep into Gaul in AD 260 and AD 268. In response, a wave of coastal fortifications was constructed or rebuilt across the region, from the Netherlands through Belgium and into northern France, including renewed works at Oudenburg and Aardenburg. Although there’s no direct evidence from Roman writers of similar attacks on Britain, it is possible the British coastal defences were erected as a precaution against the same type of threat.

Another theory suggests that these forts may not have been constructed to protect the empire from external enemies at all. From around AD 260, Britain was drawn into two periods of rebellion during which rival ‘empires’ broke away from Roman control. The first was the so-called Gallic Empire, founded by the general Postumus (ruling AD 260–69). Although the Roman emperor Aurelian reasserted central control in AD 274, a new challenger soon emerged: Carausius, commander of the Channel fleet, declared himself emperor over Britain and northern Gaul in AD 286. His regime lasted until AD 296, when his successor Allectus was defeated by forces loyal to Rome.

It’s possible that Postumus initiated the continental coastal fort-building, and perhaps even the British ones. However, archaeological evidence from sites in Britain more convincingly points to a timeframe aligned with the reigns of Carausius or Allectus.

This raises an intriguing possibility: these coastal forts may have been constructed not to defend the Roman Empire from Germanic raiders—but rather to protect breakaway British regimes from a Roman reconquest.

4th Century Forts

The prolonged period of internal conflict and competing emperors that had disrupted Britain from AD 260 drew to a close in AD 324, when Constantine I (r. AD 306–37) emerged as the sole ruler of the Roman Empire. By AD 312, he had successfully reasserted control over the north-western provinces. The fort at Oudenburg was rebuilt between AD 325 and 330, featuring wall towers similar to those found in Britain’s later coastal forts. This reconstruction may have formed part of Constantine’s broader effort to strengthen the Channel defences and could even mark the beginnings of the Count of the Saxon Shore’s command.

In Britain, archaeological finds suggest that many coastal forts on the east and south-east shores remained active throughout the 4th century. However, there is also strong evidence that some—such as Burgh Castle, Lympne, and Reculver—had been abandoned by the AD 380s. This shows how the Notitia Dignitatum, compiled around AD 390 or later, includes outdated information. Nevertheless, a few forts continued to function into the early 5th century. At Richborough, for instance, large quantities of coins dating to around AD 402 have been uncovered, along with a rare baptismal font—clear signs of occupation and Christian activity even as Roman rule was waning.

The earliest documented raids on Britain’s coast date from the 4th century. The historian Ammianus Marcellinus describes Saxon involvement in Britain from the AD 360s onward, including their part in the so-called ‘Great Conspiracy’ of AD 367.

It will be sufficient here to mention that at that time the Picts, […] and the Scots were all roving over different parts of the country and committing great ravages. While the Franks and the Saxons who are on the frontiers of the Gauls were ravaging their country wherever they could effect an entrance by sea or land, plundering and burning, and murdering all the prisoners they could take

The Roman History, Book XXVII, By Ammianus Marcellinus

This event is now thought to reflect a serious, though perhaps exaggerated, wave of coordinated attacks from northern Britain, Ireland, and the continental coast. These incursions were repelled by the Roman general Count Theodosius, who landed at Richborough and made London his operational base. The network of coastal forts likely played a key defensive role during this campaign.

A high-ranking officer, Nectaridus—described as comes maritimi tractus (Count of the Maritime Region)—was reportedly killed or captured in the fighting. His title closely resembles that of the Count of the Saxon Shore, hinting at a shared or evolving role.

During the final years of the 4th century and into the early 5th, Roman troops were gradually withdrawn from Britain to reinforce other parts of the empire. Key troop movements occurred under Magnus Maximus in AD 383 and again, possibly for the last time, under Constantine III in AD 407.

The poet Claudian celebrate the military achievements of the general Stilicho, who was a powerful commander under the Western Roman Emperor Honorius. In the poem, Claudian praises Stilicho for protecting various frontiers of the Roman Empire — including Britain — from external threats.

Next spake Britain clothed in the skin of some Caledonian beast, her cheeks tattooed, and an azure cloak, rivalling the swell of ocean, sweeping to her feet: “Stilicho gave aid to me also when at the mercy of neighbouring tribes, what time the Scots roused all Hibernia against me and the sea foamed to the beat of hostile oars. Thanks to his care I had no need to fear the Scottish arms or tremble at the Pict, or keep watch along all my coasts for the Saxon who would come whatever wind might blow.

Claudian, On Stilicho’s Consulship (A.D. 400), Book 2

By the early 5th century, the fate of the coastal fort garrisons remains unclear. Though the Notitia Dignitatum lists them, how many soldiers still manned these defences—if any—remains uncertain.

The Postioning of the Forts

The Roman forts lining the east and south-east coasts of Britain display several consistent characteristics. All were situated on low-lying terrain, close to secure anchorages at major estuaries or tidal inlets. Some appear to have functioned as strategic pairs—such as Reculver and Richborough, positioned at either end of a significant maritime channel, and Caister and Burgh Castle, located on opposite sides of a vast, sheltered estuary.

These positions offered key strategic benefits. They allowed the forts to support naval patrols, manage the transport of military supplies and communications in and out of the province, control inland access to Roman Britain via its major navigable rivers, and provide protection for commercial shipping and maritime trade routes. In these roles, the forts acted as both defensive bastions and logistical hubs.

To fulfil such duties, their garrisons needed to be agile and capable of responding quickly—ideally a combined force of infantry and cavalry. However, the Notitia Dignitatum mostly lists infantry units stationed in these forts. This raises questions about the accuracy and timeliness of its entries, especially given the shifting military needs over time.

While a Roman soldier’s helmet reconstructed from remains found at Burgh Castle points to continued military activity into the 4th and 5th centuries, the forts themselves did not all arise at once. Instead, they developed gradually across a span of roughly 70 years during the 3rd century, likely built for differing purposes in response to evolving threats. Their unification into a single military system under the leadership of the Count of the Saxon Shore—as later described in the Notitia—likely did not occur until the early 4th century, perhaps during the empire’s consolidation under Constantine I. Some of the forts included in this system may have originally been built during the rebellious reigns of Carausius and Allectus.

Though the precise origins of the Saxon Shore system remain uncertain, it is clear that at some stage these forts were integrated into a broader command structure overseen by a high-ranking military officer. While this command primarily operated in the south and east, archaeological evidence shows that Roman military construction also continued in the north and west during the same period. Today, the Saxon Shore forts stand as enduring monuments to the military and political challenges that defined the final centuries of Roman rule in Britain.