Edinburgh and the Flodden Wall

Almost directly opposite to the Covenant Martyrs' Memorial in the graveyard, is the Flodden Wall. Back in 1513, Scotland suffered a truly dreadful defeat at the hands of the English. As a result, Edinburgh built a wall around its town as a safety measure. The wall did not save Edinburgh from English (or any other) invasion. But, while it survived, it provided custom checkpoints.

As far as I know, only one part still exists, the part you can see within Grayfriars Kirkyard.