Those little glass squares embedded in London pavements weren't put there for decoration. History creator Anya Hooper, known as Anya Through Time, explained that they are pavement lights, built to bring daylight into rooms below the street. Know Your Meme covered her video on October 22, 2026.
The sidewalk had another job
In the late nineteenth and early twentieth centuries, shop basements, storage rooms and workshops needed daylight. Before electric lighting was widespread, durable glass lenses in the pavement helped sunlight reach these spaces. Some designs used prisms to direct light deeper into a room. To pedestrians the squares look like unusual tiles; to people working below, they were windows in the ceiling. The street doubled as a lighting system.
Why is some of the glass purple?
Hooper also describes a surprising color change. Older glass sometimes contained manganese compounds to counteract a greenish tint from impurities. With prolonged exposure to sunlight, certain pieces can gradually become violet. Purple is a clue to an older manufacturing process, not a precise date stamp: the recipe and exposure conditions matter too. Apparently even a sidewalk can develop a long tanning history.
What did people actually say?
According to Know Your Meme, viewers said they had always wondered about the squares, while others added information about similar features in different cities. These are the publication's summaries of responses, not comments independently retrieved word for word.
The sharpest comic contrast comes from Hooper's own public caption. Despite explaining the history, she admits that she is somehow always afraid of falling through the glass. Knowing the engineering is one thing; persuading your feet to trust it is another.
Original jokes, not social-media quotations
An imaginary planning meeting: “The basement needs windows.” “But there's a sidewalk above it.” “Excellent. Make the sidewalk the window.” “And the pedestrians?” “Free daily stress testing.”
Another invented line: “Why is the glass purple?” “A century of sunlight.” “Even the pavement has a longer tanning record than I do.” Neither joke is a real online comment.
The punchline
What looks like an odd pattern under your shoes was once a clever way to light the space beneath them. The next time you encounter these squares, you may be walking on someone else's skylight.
