The Tower Liberties were the area, within and without the walls of the Tower, which were under the jurisdiction of the Tower and independent of the City of London.
The image below is John Strype's map of 1755 (© British Library Board ‐ Maps Crace Port. 8.43)
The map shows three additional areas later added by James II’s charter of 1686.
In the area around the Tower of London you will see what look like mini headstones.
They are round headed with the initials WD, a number and a mark of three lines in the shape of an arrow head, known as a Pheon.
These are boundary markers that mark out the area known as the Tower Liberties.
They appear at first glance to be made of stone but in fact are painted iron.
Not all are iron posts, for example at the junction of Muscovy Street and Trinity Square you will find a flat marker sited in the middle of the road.