Although it isn’t exactly a building, the London Wall built by the Romans in the late 2nd century or early 3rd century is widely considered to be the oldest building in London. The Romans built the wall sometime after they established the port town of Londinium and constructed a fort in 120 CE. The wall was one of the largest construction projects in Roman Britain, measuring about 4 km (2.5 miles) long and enclosing a space of about 134 hectares (330 acres).
After the fall of Western Roman Empire, the wall remained in use by the various occupants of London. The wall was repaired often and served as the original boundary of the city of London until the medieval period. During the Great Fire of London in 1666, nearly all of the old city of London within the walls was destroyed. Nearly all of the walls remains and the seven city gates were demolished in the 18th century, but some of the original parts of the wall remain standing as protected historical landmarks.
