Ancient empires separated by both space and time have frequently resorted to building walls, fortifications, and other barriers, over long distances, to control their frontiers. Remains of a wide range of examples of these imperial frontiers have survived: from strings of forts constructed by the Inca to control the limits of their territory – such as those built in the south-eastern Bolivian Andes during the 15th and 16th centuries AD – to the linear barriers of the Sasanian Empire like the Great Wall of Gorgan – which dates from the 5th or 6th century AD and runs for 195km across northern Iran. Of these ancient frontiers, the two that are by far the most renowned are the Frontiers of the Roman Empire – of which Hadrian’s Wall and the Antonine Wall in the UK and the Upper German–Raetian Limes are the best-known segments – and the Great Wall of China – for which the iconic sections located to the north of Beijing, constructed during the Ming Dynasty (AD 1368-1644), figure prominently in the popular imagination. Here we compare these two famous frontiers, both of which are World Heritage Sites, in terms of length, scale, and some aspects of their historical development. Although separated by more than 4,000km, and conceived within entirely unconnected historical contexts, there are many similarities in the solutions at which both Roman and Chinese emperors, and their wall-planners, arrived in order to exercise control over the edges of their empires.
The Great Wall
What most people think of as the ‘Great Wall of China’ is, rather than one continuous barrier, a complex system encompassing many separate walls with both attached and free-standing towers, forts, ditches, and other infrastructure – all of which were constructed during multiple phases across different historical periods. The earliest of these walls, known as the ‘Chu Great Wall’, runs for more than 300km in Henan Province and is thought to date from the mid 7th century BC. Even at this early date, this was not simply a linear barrier, but included beacon-towers spaced at intervals between 2.5km and 4km apart – to carry signals along the frontier – and a network of nearby forts and fortified towns. Such features, along with others, were incorporated into the many phases of wall-building that followed. By the Ming Dynasty, the frontiers had grown in complexity and included systems of beacon-towers, ditches, obstacles to break cavalry charges, projecting sections from which defenders could overlook attackers, systems of forts and fortresses from which troops could be rapidly deployed, and fortified passes where people and goods entering and leaving Chinese territory could be controlled. By the end of Ming rule, these defences ran from Hushan, Liaoning Province, on China’s north-eastern seaboard, west to Jiayuguan, Gansu Province, on the edge of the Gobi Desert.
Although the complex nature of the Great Wall has long been appreciated, precise figures have only become available relatively recently. In 2012, a survey of these ancient walls, as part of a project to quantify the surviving remains and identify conservation issues, calculated that they stretch along 21,196km and comprise more than 40,000 different monuments. This includes more than 10,000 distinct sections of wall, more than 1,700 ditches, 2,211 forts or fortified passes, and more than 29,000 individual buildings. Of these stretches of wall, roughly 15% were constructed during the pre-imperial Spring and Autumn and Warring States periods (8th century-221 BC), a further 17% during the subsequent Qin and Han dynasties (221 BC-AD 220), 19% over the course of the dynasties that followed until the foundation of the Yuan Dynasty (AD 1271), and 42% during the Ming Dynasty (AD 1368-1644). Along its length these different sections of wall traverse a wide variety of environments and types of terrain, with the materials and methods of construction differing accordingly: from the rammed earth of those sections constructed during the Han Dynasty across western China to the fired bricks of the Ming walls in Hebei Province. Far from a uniform barrier, what we today call ‘the Great Wall’ is a monument made up of many different stretches constructed at different times from different materials with different purposes in mind.
The Frontiers of the Roman Empire
The frontiers of Rome were similarly formed of various elements: linear barriers, which were actually rather rare, as well as forts, fortlets, and towers, usually protected by ditches. Like the Great Wall, these structures were erected at various dates, though over a much shorter timescale.
Unfortunately, there are no detailed surveys of all Roman frontiers to allow an exact figure to be produced. Spurred on by the precise figures produced by Chinese scholars, we have undertaken an exercise to try to achieve a more accurate figure for the length of Rome’s frontiers. This was not an easy exercise. Across the northern half of the empire, the frontier was formed by three great rivers: the Rhine, Danube, and Euphrates. They twist and turn and, moreover, have been straightened or dammed since the Roman period, so obtaining an accurate calculation is not straightforward. Much of the frontier in the southern half of the empire lay on the edge of deserts, offering a different issue, for here the line of the frontier is difficult to define. To these problems, we may add that the use of maps of different scales produces different answers. Measurements based on those in the maps in Breeze’s Frontiers of Imperial Rome (see ‘Further reading’ box), for instance, lead to a figure 10% less than larger-scale maps.
Furthermore, as in China, the line of the frontier changed over time. Which date then should be selected to define the frontier? Maps too often depict the empire at its greatest extent – that is, under Trajan (AD 98-117). But this lasted only three years, before his eastern conquests were abandoned. The reign of Hadrian (AD 117-138) is a better choice. He consciously stopped the expansion of the Empire, but could not control the actions of his successors. Antoninus Pius (AD 138-161) advanced the frontiers in Britain and Germany while, a few decades later, Septimius Severus (AD 193-211) expanded the empire in North Africa and the east, and sought to do the same in Britain. It was at this point that the Roman Empire reached its widest extent. Nevertheless, the reign of Hadrian is probably a better time to undertake a survey of the length of the frontiers of the Roman Empire. We calculate the total lengths of the frontiers of Rome at that time to be about 13,000km. This figure, it must be emphasised, was arrived at using ‘traditional’ methods; there is no doubt that a more-accurate measurement could be achieved using modern techniques, such as the highly accurate drone-based surveys used to calculate the length of the frontiers in China.
Chinese scholars reached the total length of the Great Wall, 21,196km, by adding together the lengths of all the different sections. These frontiers were not all in use at the same time, rather like the various frontiers of the Roman Empire. While it is possible to propose a comparable figure for the frontiers of Rome, this would require detailed analysis and fail to represent any historical reality. Adding up all the frontier lines that were in use for the 150 years from the time of Hadrian to the accession of Diocletian would certainly produce a different figure than 13,000km. For example, there was a new frontier in the upper reaches of the Rhine and Danube – the Danube–Iller–Rhine line – but, to balance that, Dacia and its 1,000km-long frontier had been abandoned.
This has been an interesting exercise. It reminds us of the great complexity of frontiers: they were certainly not static creations. Even so, the figure of 13,000km remains the most-useful figure for the total length of the frontiers of the Roman Empire at its height.
Going the distance
The Frontiers of the Roman Empire and China’s Great Wall were both impressive systems that brought together physical infrastructure and human effort to control the limits of imperial authority across huge geographic areas. As frontier systems, they had some common features – a network of towers by which signals could be transmitted, forts manned by imperial soldiers, and fortified passes that allowed the regulation of people and goods travelling from one side of the frontier to the other. In military terms, their effectiveness can be debated – typically the Chinese dynasties that constructed walls were brought down by internal troubles rather than foreign conquest and, in the cases where external forces – the Mongol Yuan and Manchu Qing armies – did invade, the walls failed to halt their progress, just as the Roman frontier troops failed to prevent the invasion of Gaul by the Alans, Suebi, and Vandals in 406. From a long-term perspective, the Chinese frontiers developed over a much longer period than those of Rome – which sprang up and fell out of use in just a few centuries compared to at least 2,000 years of Chinese wall-building. Both, however, allowed some of history’s largest and most powerful empires to state clearly their intent to rule – often troublesome – frontier zones, control movement through their territory, and establish a deterring – if not impenetrable – obstacle against would-be attackers.
D J Breeze (2019) The Frontiers of Imperial Rome, Barnsley: Pen and Sword.
D Frye (2018) Walls: a history of civilization in blood and brick, London: Faber & Faber.
A N Waldron (1990) The Great Wall of China: from history to myth, Cambridge: Cambridge University Press.
For more information, visit the website www.greatwallheritage.cn.