Three sections of a huge but little-known Roman wall, discovered under the City of London, have been given protected status as scheduled national monuments. The riverside wall was a once vast stone structure that formed part of the defences of Roman London. Built in the third century AD along the Thames, it connected to the city’s landward fortifications, large sections of which still exist. Much of it has been lost in the intervening 1,700 years and the wall was all but forgotten, although one section survived around the Tower of London. During excavations by Mola (Museum of London Archaeology) between 2006 and 2016, however, three substantial new stretches were discovered. They have now been added to the National Heritage List for England, which means they have been designated as nationally important sites and given protection from any future development. Duncan Wilson, the chief executive of Historic England, said: “Even in a really dense city like London, built up over 2,000 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 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.” Jane Sidell, Historic England’s principal inspector of ancient monuments for London, agreed that the riverside wall was “slightly eccentric”. While its original position is known, running between what is now Blackfriars station and the tower, it was built at a time when the city relied on its busy Thameside wharfs. “By sticking an enormous great wall on the waterfront, you interfere with free and easy access between the boats,” she said. “So the riverside wall is slightly strange, because it causes this problem with trade. So we still don’t know how it worked. We don’t know whether there are gateways in the riverside wall. We don’t know how people got through it.” While partly defensive, she says, it may have been partly built as a legacy project by an ambitious governor wanting to leave his mark on the city. In parts, the wall incorporates reused stones that had previously been Roman monuments, shedding more light on architecture and building techniques from the period. The new protection also covers several exceptionally preserved wooden wharf and quay structures from both the Roman and medieval periods. At one site, beside what is now Upper Thames Street near London Bridge, a 20-metre stretch of stone wall was found, some of it 1.4-metres high, alongside a succession of timber Roman quays, used for loading and unloading cargo from boats. Two further sections of wall, measuring 45 and 35 metres, were found a little to the east, one of which reused a wooden cornice or pediment from a building, thought to be unique in Britain. All three stretches of wall have been left in situ and are now under modern buildings. Though not at risk now, they could be in 40 or 50 years given the frequent redevelopment of sites in the City, Sidell said. “The protection that we have given now is for the future. To identify that the riverside wall is nationally important, and something that needs to be protected.”