The Road Over the Top: Castleshaw and Slack Roman Forts and the Mystery of Cambodunum

16 minute read time.

Carving a Way Through the Uplands

If you stand on the Pennine Way, near Standedge and look down across the Castleshaw Valley in Saddleworth, it is still possible to imagine the land as it was in Roman times. But nineteen centuries ago, there would have been more deciduous woodland clinging to the lower slopes of the hills and plenty of peat-bog and heather on the gritstone moorland. Wolves, brown bears and wild boar would inhabit the region and, in the first century AD, this same landscape carried a high-level route across the Pennines. Roman governor Gnaeus Julius Agricola ordered the construction of key military roads and a network of forts throughout northern England during his campaigns between AD 79 and 84.

Military Network & The Pennine Frontier

The Roman road network linked major legionary fortresses, each housing around 5,000–6,000 soldiers, with prosperous towns and coastal ports. These routes were secured by a system of auxiliary forts (typically 500–1,000 men), smaller fortlets (50–80 men), and watchtowers, ensuring the protection of supply lines and the control of local populations.

In the north, Rome drove a military highway directly through the hostile Pennine landscape, linking the key legionary bases of Deva Victrix (Chester) in the west and Eboracum (York) in the east. This route cut through the territory of the Brigantes, one of the most powerful tribal groups in Britain.

Road Engineering & Drainage

Roman roads were engineered by digging a trench to solid ground and building upward in layers: a base of large stones, smaller stones mixed with mortar, and a fine gravel or sand foundation. The top layer consisted of tightly fitted paving stones 6-12 inches thick. This durable surface featured a gentle curve (camber) to channel rainwater into drainage ditches either side, keeping the road stable for centuries, through heavy use and harsh weather. Many still serve as modern road foundations today.

Roman soldiers generally wore only their wool tunics and hobnailed sandals when building roads. However, in hostile territory they also kept on their armour in case of attack. This is reflected on Trajan’s Column, where soldiers engaged in construction work are shown wearing armour. In bad weather, they would drape a thick, water-resistant wool cloak, known as a sagum, over their shoulders. The only item they might remove was the helmet, though even this had to be secured to them or kept close at hand. What a gruelling task it must have been!

The Saddleworth Route

The Trans-Pennine highway passed through the landscape of West Yorkshire along a specific corridor:

Austerlands to High Moor: Entering Saddleworth from the west, the road passed just north of Austerlands and maintained a straight alignment, past Thurston Clough, up to High Moor, from where both Manchester and Castleshaw are visible.

Knott Hill & Delph: At High Moor the road turned, navigating the steep, difficult side-slopes of Knott Hill before crossing the River Tame at Delph and proceeded in a straight line to Castleshaw.

Castleshaw to Slack: From Castleshaw, the road climbed eastward out of the valley basin to Standedge, and just after crossing the Pennine ridge, it passed Worlow Edge on Pule Hill, where archaeologists discovered the remains of a Roman watchtower and signal station…then on, via Marsden, to Slack, near Huddersfield.

The Terrain: the Pennine Landscape Today

Photographs © Christine Widdall More Photos at this Link

Protecting the Route

A road was only as safe as the troops who guarded it. A marching army, or an imperial courier, could not afford to spend a night exposed on the open moors, at the mercy of the local Celtic tribes and the weather, so the Romans established a chain of interlinked outposts to the east of Manchester.

To understand how Rome managed this route, we can consider two outposts that served their requirement: the bleak western gatehouse to the hills at Castleshaw, in Saddleworth and the busy, eastern fort and settlement at Slack, near Outlane, Huddersfield. Carefully spaced just one day’s march apart, their different histories tell the story of a developing frontier and reveal how Rome adapted to the challenges of the unpredictable Yorkshire weather and to their changing military requirements.

The Western Gatehouse: Castleshaw 1

If you drop down from the top of Standedge into Saddleworth, just above Delph, you’ll see a shallow hill rising above a natural hollow at Castleshaw. Around 79 AD, a Roman auxiliary fort was constructed at this site to control the highway and the western approach to the Pennine pass.

The original fort, Castleshaw 1, possibly replaced a Brigantian hillfort. The 2nd-century geographer Claudius Ptolemy recorded a settlement called Rigodunum (meaning “royal fort”) in the vicinity…and more recently, researchers have accepted Castleshaw Fort as being Rigodunum. [Other sources have suggested that Rigodunum was at Elslack, but that fort is known by the Roman name “Olenacum”.]

Castleshaw 1, covered roughly three acres, with turf and clay ramparts, timber buildings, and deep defensive ditches, and accommodated about 500 soldiers from an auxiliary cohort, along with perhaps a centuria of cavalry, around 100 men. Roof-tile stamps indicate that Cohors III Bracar-augustanorum, troops from Pannonia along the Danube, serviced the site. In Daycroft Field to the south of the fort, evidence has been found of a small civilian settlement, a vicus, with agricultural activities.

Castleshaw Becomes a High-Altitude Border Post: Castleshaw 2

However, frontiers are fluid things. By 105AD, the wild Celtic tribes of the Pennines were no longer the active threat to the state that they had once been. So, around 105 AD, the Roman military command faced a decision: how do you continue to manage a territory in the Pennines that is no longer an active war zone, but remains a vital transit route that needs protecting? The answer, at Castleshaw, was downsizing.

The Romans dismantled the large fort and replaced it with a small, heavily fortified fortlet, tucked inside the site of the old fort. Covering less that one acre and constructed within the southern boundary of the original fort, it marked the end of large garrisons in the Saddleworth hills.

The archaeology of Castleshaw 2 fortlet reveals its purpose. There was one barrack block, workshops, a granary big enough to withstand a siege, and an administration building. It housed only a small detachment, perhaps 50-60 soldiers, who were likely rotated from larger bases at Mamucium (Manchester) or Slack on a regular basis.

The fortlet became more of a supply post, border checkpoint and fortified post-office. It guarded the mouth of the pass and maintained the cursus publicus (the imperial courier network), ensuring that official correspondence could travel between York and Chester without being ambushed by gangs of local tribesmen.

Castleshaw, Site of the Abandoned Fortlet

Below left: the ditch along the south side. Centre: the fortlet from the north-west corner. Right: aerial view from the west.

Castleshaw 2 was abandoned between AD 120-130. Archaeological evidence suggests that, around this time, the civilian settlement was deliberately burned and cleared.

As the Roman Empire consolidated its northern frontier, the defensive line had shifted to a corridor of roads and forts stretching across northern England from Carlisle to Corbridge. When Emperor Hadrian arrived in Britain in AD 122, he ordered the construction of his great stone wall, establishing a fixed frontier from west to east. In the following decades, Roman troops were redeployed north from the Pennines, and under Hadrian’s successor, Antoninus Pius, the frontier advanced again. A new wall, the Antonine Wall, was constructed further north between the Firth of Clyde and the Firth of Forth.

Just for fun…

Just for fun (because history must surely be fun)…let’s imagine how the fort and later fortlet might look today, if some great benefactor built a massive pseudo-Roman visitor centre. There are some variations and artistic licence, though the layouts do follow Ken Booth’s diagrams in his book “Roman Saddleworth”.

Castleshaw 1 – The Flavian Fort, built c79 AD

Castleshaw 2 – The Trajanic Fortlet, built c105 AD – abandoned by c130 AD

The Fort at Slack: The Beating Heart of Rome in the Pennines

For the soldiers stationed at Castleshaw, watching the drenching rain sweep across the moors, from a fort perched high on the edge of the valley, must have been a lonely, miserable existence. The real engine of the Pennine frontier hummed a few miles to the east, over the tops at Slack, where the climate was just a little milder and dryer. They must have looked forward to rotation.

The fort at Slack, just over the ridge near Outlane, Huddersfield, was Rome’s beating heart in the Pennines and was designated a castellum, a military camp. While the military presence at Castleshaw was being reduced to little more than a border checkpoint, attention had shifted east to Slack. Here, the slope of the land eases, offering space for something far more substantial than a lonely outpost. Slack was developed to be the administrative and industrial heart of the high country…and outside the fort was a bustling civilian settlement.

In 1743, archaeologists unearthed the foundations of a temple and altar. But the true scale of the site only became apparent through the excavations of the nineteenth and early twentieth centuries. Work in 1865 revealed the remains of a substantial residence arranged around a courtyard. Further campaigns, between 1913 and 1915 and again from 1958 to 1963, uncovered the fort’s ramparts along with the foundations of its gateways and corner towers.

The ultimate symbol of Roman prosperity in the Pennines was the Slack Bathhouse. Discovering a sophisticated bath complex on the edge of the moors was an amazing experience for the archaeologists. Excavations revealed an elaborate suite of rooms equipped with an underfloor hypocaust heating system, where hot air from a wood-fired furnace circulated beneath raised tiled floors.

Travellers marching across Standedge would have experienced a dramatic contrast. They would have started their day at Castleshaw, a strictly managed military watchtower and checkpoint, where they had stayed overnight. After a few hours of marching through the heather and bogs the next day, they would descend into the noisy, vibrant frontier town at Slack, where the air smelled of smoke and roasting meat, and the luxury of the bathhouse beckoned.

Imagine the scene: outside, the Pennine sleet and snow is driving across the hills; inside, off-duty soldiers, administrators and travellers are sweating in the caldarium (hot room), scraping off the gritstone dirt and plunging into the frigidarium (cold pool). Far more than a place for hygiene, the bathhouse functioned as a vibrant social amenity, a blend of a modern gym, public house, and luxurious health club that provided a democratic meeting place, where different social classes could interact and make connections.

The Tiles That Built the District

The bathhouse at Slack owed its comfort to a substantial local industry. In the nearby Grimescar Valley at Fixby, soldiers of the Fourth Cohort operated an extensive tilery. A rectangular kiln, unearthed at Grimescar Woods during excavations in the 1950s and 1960s, measured about 3×4 metres and was dug into the bedrock, produced roof and floor tiles as well as pottery. Large quantities of clay tiles and bricks were fired in high-temperature kilns, stamped with the unit’s mark, COH IIII BRE, and then transported up the hillside for use in constructing the fort, its granaries, and the bathhouse.

What would a reconstruction of the Slack Fort look like?

The Slack fort was situated alongside the modern day M62…in fact the M62 was built over part of the Vicus (civilian settlement outside the fort). It would have been an impressive sight.

Let’s, for a few moments, go back in time again. I’ve shown reconstructions alongside modern buildings and the M62 where the traffic is closely following the old Roman Road. Enjoy it for what it is, then we’ll take a look at what life was like for a soldier living there, because most of the year it isn’t sunny!

The Life of a Roman Soldier in the Pennines

Whether on guard at a lonely fortlet like Castleshaw or working in the busy settlement at Slack, a soldier’s life was defined by discipline, labour, and constant readiness. Life for the soldiers was far from idle. Of course there was some fighting at times, but there were also long periods of mundane work. In addition to operating the tilery, their days at Slack were filled with routine duties, such as standing guard, construction work and roadbuilding, patrolling and repairing defences. Even the bathhouse needed constant attention, with men assigned to maintain it.

Not all soldiers carried out the same tasks. Some specialised in particular roles: the armourers would maintain weapons and equipment, butchers prepared food supplies, medics treated injuries and illness, clerks kept records and accounts, and some soldiers trained and cared for horses. These men were collectively known as immunes, soldiers who were exempt from the more basic, repetitive labouring duties.

But there was down time too. When the day’s duties were done, the soldiers turned to other diversions, such as wrestling, boxing, or playing a frantic ball game called harpastum that looked more like training for battle than play. Roman soldiers, even on remote frontiers, spent a surprising amount of their spare time playing board games. These weren’t just for fun; they helped pass long hours, build friendships, and even sharpen military thinking. Dice rattled across wooden boards, wagers were laid and lost, and soldiers bent over rough boards, playing simple games like latrunculi, where small glass counters trapped and outplayed each other like armies on a battlefield.

Even on the western edge of empire, the soldiers were never entirely cut off from friends and family. Letters, written on papyrus or wax tablets, were passed along the road between the forts; requests for supplies or news to and from home. One soldier, famously writing from the northern frontier, simply asked for “socks, two pairs of sandals and two pairs of underpants”, a small but revealing reminder of life in the cold and damp of Roman Britain.

What happened to the settlement at Slack when the soldiers left?

For many years, historians believed that Slack was completely abandoned around AD 142, when Cohort IIII Breucorum, the formidable auxiliary infantry unit from the Balkans, moved north to serve on the Antonine Wall. However, the community they left behind did not simply disappear.

Outside the fort ramparts lay the vicus, the sprawling civilian settlement populated by traders, artisans, beer-sellers, and labourers. As the military presence scaled down, industry is what kept this settlement alive. While Castleshaw declined and became deserted, Slack was still the processing centre for the region. It was where iron was smelted, where cattle from the hills were traded, and where the logistics of the Chester-to-York highway were managed, and the settlement prospered into the late third century.

Incredibly, the M62 now cuts straight through the old Roman site, burying part of it under tarmac and splitting what was once a single settlement into separate areas.

The Mystery of Cambodunum on Iter II

The Antonine Itinerary, a register of routes across the empire, is often praised for its accuracy. Mostly, it does a good job of mapping out Britain’s Roman road network. But there’s one place where things stop adding up. If you try to follow Iter II today, tracing the route from York to Manchester across the Pennines, you’ll quickly run into a problem.

According to the record, the journey should be straightforward:

• 9 miles from Eboracum (York) to Calcaria (Newton Kyme, nr Tadcaster)
• 20 miles onward to a place called Cambodunum
• 18 miles more to Mamucium (Manchester)

Simple enough. But once you try to plot that route on a modern map, the numbers completely fall apart. The distance between Tadcaster and Manchester, following the likely line of the Roman road, is far longer than the 38 Roman miles given in the Itinerary. In reality, it’s closer to 60 Roman miles (roughly 55 modern miles). That leaves a massive gap of 22 Roman miles unaccounted for…also the distance from Slack to Manchester is more like 28 Roman miles, not 18…something is very wrong.

So what’s going on? Did the Romans mis-measure the route? That seems unlikely as they were capable surveyors. There are other possible explanations. One possibility is a simple copying error. The text we have today was transcribed centuries after the Roman period, and small mistakes could easily creep in. Two similar names, Cambodunum and Camulodunum, appear in different versions of the route. It’s not hard to imagine a tired scribe making a typo… accidentally skipping a line or merging entries for two places with similar names. If either happened, an entire staging post, and its distance, could have vanished from the record for ever.

Is there a Lost Fort between Tadcaster and Slack?

At the heart of the mystery is the fort at Slack. For years, it was identified as Cambodunum. It made sense geographically: it sits neatly on a known Roman road and occupies a strong strategic position. But there’s a catch. Slack is simply too far from Tadcaster to match the 20 miles given in the Itinerary. If Slack is Cambodunum, then the Roman distances don’t work. If the distances are right, then Slack is not Cambodunum after all. In fact, the Ordnance Survey Roman Map of Britain now names Slack as Camulodunum.

So it’s likely that there was another staging post between Tadcaster and Slack. The “missing stop”, Cambodunum, would fall somewhere near Leeds. Adel has been suggested, given the evidence of significant Roman activity there, but Adel is on the road from Tadcaster towards Ilkley. Others have pointed to potential sites in the Spen Valley, near Cleckheaton or Heckmondwike. Recently, LIDAR scans of the region (Light Detection and Ranging) have revealed a portion of Roman Road at Fixby, which has been determined to come from the direction of Slack…and a route onwards from there towards Cleckheaton would make sense. So far, though, there’s no clear archaeological evidence tying any of these locations to Cambodunum. It’s a real teaser!

What makes this stretch of Iter II so fascinating is that it remains unresolved. The numbers don’t quite work, the archaeology doesn’t give a clear answer, and every explanation has its problems. Somewhere in the hills of West Yorkshire, there may still be clues waiting to be found.

The name Cambodunum, alias Campodunum, also appears in early Anglo-Saxon history (recorded by the historian Bede). King Edwin of Northumbria had a royal estate and an early Christian basilica there in the 7th century, which was destroyed in AD 633. It is speculated that was at Barwick-in-Elmet, 9 miles SW of Tadcaster.

One Corridor, Many Centuries Apart

There’s a striking similarity in how people move across northern England today. Modern transport may seem like a triumph of engineering, but when we cross the Pennines today, we are following routes laid out nearly two thousand years ago. The Roman Road from Manchester, through Castleshaw and Slack eastwards towards Leeds, is the ancestor of the A62 and the M62.

The reason is simple: geography. Only a few natural passes cut through the gritstone hills without extreme gradients. When Roman engineers looked out across bogs, rocks, and steep valleys, they chose the easiest route…over Standedge.

Centuries later, civil engineers did exactly the same. The Huddersfield Narrow Canal, the railway, the A62, and M62 all follow this corridor, linking east and west through the most practical route. The purpose hasn’t changed: to move people and goods efficiently across difficult terrain.

• c.79 AD: Roman soldiers march at 100-120 paces a minute (about 3 miles per hour), through rain, mist and wind, from Castleshaw, towards the fort at Slack and on towards Eboracum.

• 2026 AD: Lorries rumble across the same landscape, sometimes at 60 mph, sometimes no faster than the Romans, carrying freight from Liverpool to the Humber.

Different era, same journey.

So, the next time you sit in a traffic queue on the M62 near Outlane, watching the fog roll low over the moors, look out across the hills towards Slack and go back in your mind to the Roman Road. The mode of transport has changed, the average speeds have increased, but we are still using Agricola’s highway to get home.

© Christine Widdall June 2026