Hadrian's Wall is an ancient Roman fortification located in northern England. When built, it was 73.5 miles (117 km) long, spanning the entire width of Great Britain. Hadrian's Wall was built around 122 to 130 CE and served many functions for the Romans. It was a visible symbol of their might, the northern border of the Empire, defense against the Picts of ancient Scotland, and a trading center. Today, much of the wall survives, though many parts are eroded and its stones have been culled for other building projects over the centuries.

Construction on Hadrian's Wall began after the Emperor Hadrian visited Britain in 122. Civil problems in other parts of the Empire, notably in the Middle East, inspired Hadrian's decision for a massive fortification in Great Britain. The width and height of Hadrian's Wall varied along its length, but generally ranged from three to six meters (10 to 20 feet) in most places. It was constructed of stone and turf.

Hadrian's Wall incorporated milecastles, or small forts, at every Roman mile, for a total of 80 along its full length. Intermediate turrets were also included for observation. Later, a number of larger forts, from 14 to 17 depending on the source, were built near the wall for additional protection. A Vallum, a large ditch with high earth banks on either side, was added to the southern side of Hadrian's Wall.

Hadrian's Wall was occupied by auxiliary Roman troops throughout the remainder of the Roman presence in Great Britain, and it is assumed that many intermarried with the native population. The emperor after Hadrian, Antoninus Pius, turned his attentions to the construction of a new wall, the Antonine Wall, within Scotland, and Hadrian's Wall was not heavily used during his reign. It became important again in the reign of the new Emperor, Marcus Aurelius, after Antoninus Pius' attempts at northern expansion were unsuccessful. Roman forces withdrew from Great Britain early in the 5th century, though Hadrian's Wall remained occupied in parts for a few decades. Today, Hadrian's Wall is a UNESCO World Heritage Site and the most popular tourist attraction in northern England.