The famous wall built to protect the Roman Empire from invasions is Hadrian's Wall. Constructed under Emperor Hadrian around AD 122, this fortification stretched across northern England, marking the northern limit of the Roman Empire. It served both as a defensive structure against invasions from tribes to the north, particularly the Picts, and as a means of controlling trade and migration. The wall included a series of forts, towers, and smaller milecastles, allowing Roman troops to maintain a presence in the region. Today, it is a UNESCO World Heritage Site and remains a testament to Roman engineering and military strategy.