New protection for Roman London’s ‘enigmatic’ riverside wall

Three recently uncovered sections of the massive and “enigmatic” riverside wall of Roman London have been protected as scheduled monuments.  

The mile-long wall was built in the mid or late third century and enclosed the city by running parallel to the Thames shoreline and connecting the ends of the two-mile land walls at today’s Blackfriars and Tower Hill. It stood about 15ft high (4.5m) and 7ft (2m) across.

With the wall seemingly built in a hurry, using stones recycled from demolished buildings, archaeologists remain unsure about what prompted the drastic action, although there are tantalising theories. The newly recorded stretches have been left in situ under modern buildings and experts predict that further sections — and dating evidence — will be unearthed as a result of future construction projects.

Roman London, or Londinium, developed at an important crossing point over the Thames where the river was still navigable by ships. It was a bustling port within years of the Claudian invasion of 43AD — decades before it became the provincial capital. This led to the construction of a succession of docks and wharves over the following 200 years.

According to Historic England’s new entries in the National Heritage List for England, the port’s fortunes changed abruptly with the building of the riverside wall. The authors write: “This seems to have severed the connection to the quayside, which was no longer maintained, indicating that protection of the city now took priority over river trade.”

Previous studies have suggested the port was already in decline due to falling river levels and broader economic issues. The third century was a time of turmoil across the empire, blighted by civil wars, plague, famine and barbarian incursions.

Archaeologist Dr Jane Sidell, principal inspector of ancient monuments at Historic England, said the riverside wall may have been erected solely for defensive purposes, or to enhance the status of the provincial capital as well.

She added that it was even more mysterious than the land walls, which have generally been dated to about 190-225AD. Large chunks of the land walls can still be seen at sites including Tower Hill and its contours gave shape to the City of London, or Square Mile, as it endures. Its construction emphasised London’s importance and may in addition have been intended to protect against rebellious Britons or mutinous legions.

“The riverside wall was built a bit later and we don’t know why,” Sidell said. “It’s really enigmatic.”

Unlike the land walls, which were uniformly built in Kentish ragstone and bands of tiles, the riverside wall incorporated large quantities of masonry from older structures including civic buildings — signalling broader upheavals in the city.

Analysis of its oak foundation piles helps with approximate dating. However, Sidell said: “We don’t have a firm dendrochronological [tree-ring] date for it. You need bark edge to get a good dendro date and bark edge didn’t survive on the timber piles underneath the wall. We’re thinking around the 260s or 270s.”

If that is correct, the riverside wall may have been built when Britain was part of the Gallic Empire — a breakaway state comprising Gaul and other western provinces — from around 261-273. Alternatively, it may have been the work of Emperor Aurelian, who won back those territories to central imperial control, or Probus — another strong emperor, who ruled from 276-82. One study has suggested it was built by Aurelian or Probus as part of a efforts to reassert authority

Sidell said it was also possible that the wall dated from the Carausian period. Carausius was an alleged former pirate who ruled a breakaway state in Britain and northern Gaul in 286-293. Historian and archaeologist Dr Simon Elliott has argued that Carausius or his assassin and successor Allectus built the wall as part of defences against invasion by legitimate imperial forces. It failed, if so, as Allectus was defeated by Constantius Chlorus, the father of Constantine the Great.

Barbarian incursions might seem to offer another possible motive. Saxons and Franks raided along Britain’s east coast during the later 3rd century. However, Sidell said there was no no evidence of raids up the Thames at this period that might have precipitated extreme measures.

For now, she believes we should view the wall broadly as a product of troubled times. She said: “There were several periods of unrest in the third and fourth centuries, partly driven by unrest in the other provinces and partly by pandemics and economic problems. There was a general unsettledness in the empire and I suspect the wall was a speculative defence, rather than a response to any one event.”

In the third century, the Thames shoreline was about 330ft (100m) inland of its current position and the riverside wall ran just south of the line of today’s Upper and Lower Thames Street.

The three sections that have been newly listed as scheduled monuments — at Riverbank House on Upper Thames Street and Sugar Quay and Three Quays on Lower Thames Street — were excavated by MOLA (Museum of London Archaeology) in 2006-2016.

The protective listings don’t only cover the sections of wall but also other remains at the same sites, including Roman timber quays in exceptional states of preservation. At Sugar Quay, a 148ft (45m) stretch of wall was recorded. The dig also uncovered a substantial “box quay” — made of oak timbers and filled with rubble — dating to about 133AD during the reign of Hadrian.

Explaining the reasons for the new listing, Sidell said: “There is no threat at the moment, but, because of the pace of development in the City of London, in 40 or 50 years time the buildings they’re currently under will come down and be redeveloped.”

She said that, given the scale of new construction, it was inevitable further stretches of wall would be uncovered and likely they would shed more light on its story. “New elements of the wall will turn up. And because this research has been done and because of the great excavations by MOLA, we really understand why it’s important.”

She added: “One of the reasons we protect these sites even when you can’t see them is that they’re part of a long tradition of the development of the city and they show there is a certain permanence. So even though these remains are small, there is that stability. London has been here for 2000 years and we’re optimistic it will be here for another 2000. And that can give a little bit of comfort to people in rather turbulent times.”

The sites now have the same level of protection and recognition as another section of the riverside wall at the Tower of London. 

Duncan Wilson, Historic England’s chief executive, said: “Even in a really dense city like London, built up over 2000 years, there are still mysteries to be revealed right beneath our feet. The riverside wall remains an intriguing element of Roman London which raises almost as many questions as it answers. The construction of the riverside wall effectively cut off the once bustling port, but why? It seems to suggest a major move towards defence at a time of uncertainty for the Roman provinces. 

“By adding these sites to the National Heritage List we recognise their national significance, and can closely manage their conservation so that they remain part of London’s rich story.”