Hadrian's wall is a stone and turf fortification 75 miles long across the breadth of Great Britain.
It was begun in 122 AD during the reign of Roman emperor Hadrian and was the northern border of the Roman Empire on that island for most of the Roman Empire's rule; a similar fortification made of turf (the Antonine Wall runs between the Clyde and Forth estuaries in Scotland. As well as being less sophisticated, it was occupied for a far shorter period of time as waste and corruption forced the Romans to fall back to Hadrian's Wall.
Public Domain Map ~235 miles high. Courtesy Xerox PARC.
Red Mark shows approximate location of Hadrian's Wall