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. 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.

PHOTO: P J Brown.Īlthough the complex nature of the Great Wall has long been appreciated, precise figures have only become available relatively recently. Comparing this to the Ming Great Wall at Jinshanling illustrates how varied the appearance of different stretches could be. Remains of the Han Dynasty Great Wall, constructed of rammed earth, roughly 85km north-west of Jiayuguan, Gansu Province.

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. 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. Such features, along with others, were incorporated into the many phases of wall-building that followed. 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. 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. 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. This, though, is just one of the most-celebrated stretches of an incredibly long and complex monument. Here we see an iconic stretch of the Ming Great Wall, constructed of fired brick, at Jinshanling in Hebei Province. The Great Wall of China can be truly spectacular. 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. 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. 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.

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. 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.

Roman vallum