Locksmith Monument: The Column Built To Remember And To Measure

The Monument commemorates the Great Fire of 1666. Its designers, Christopher Wren and Robert Hooke, quietly built in a second purpose far less obvious than remembrance. Both men were active members of the Royal Society, and they shaped the column into a working scientific instrument. A laboratory sits in the cellar. The shaft running up through the column is hollow by design, suited to pendulum experiments. Even the staircase carries precision in its build: the steps measure exactly six inches high, doubling as a tool for pressure experiments. A trapdoor near the top once let someone use a telescope from inside the structure itself.

That original purpose hasn't entirely faded into history. As recently as 2020, researchers from Queen Mary University of London used the Monument's own shaft to measure deformation in a hanging wire, putting a three-century-old design feature back to genuine scientific use.

An Inscription That Couldn't Make Up Its Mind

The column's own base tells a second story, carved in stone and then argued over for a century and a half. In 1681, amid the panic of the so-called Popish Plot, someone added a line blaming Catholics directly for starting the fire. When the Catholic James II took the throne in 1685, workers chiselled that line away. When the Protestant William and Mary succeeded him in 1689, they carved it back in. The dispute only ended in 1830, after Catholic Emancipation, when the line finally came off for good.

So this column has spent its whole existence doing two jobs no visitor would guess from street level: quietly measuring the world, and silently recording London's shifting religious politics in its own stonework. We're concerned with something considerably simpler. We just want the locks on whatever's nearby to keep working properly, whatever century their own history happens to date from.