Ponzo Rails
Ponzo Rails — 2026, generated SVG, dimensions variable · Geometry · Still
After Mario Ponzo, 1911
Which bar is longer?
Which horizontal bar is longer, top or bottom?
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Reveal the answer
The top and bottom bars are the same length.
↑ The mechanism, made visible.
Notes — why it looks that way
What is happening
Look at the top bar, then move your eyes to the bottom one — does the impression of its width change? There is no three-dimensional object anywhere in this figure. It is simply two lines of equal length drawn on a flat plane. The vertical guides in the answer view show that both bars’ endpoints sit at the same positions.
Why it looks that way
Converging lines act as a distance cue, resembling a road receding into the distance. Your visual system judges length within that context, so lengths that are identical on the page can look different. This isn’t just a correction for perspective — the relationship to the surrounding context is involved too.
How to check
Hide the surrounding lines and compare whether the impression of length changes. Even if the bars alone look the same, the difference can return once the context comes back. It’s not a wrong answer if your perception doesn’t change either way.
See another geometric illusion
First described
After Mario Ponzo, 1911
Media — images and data
- OG / X (1200×630)
- Instagram square (1080×1080)
- Shorts / Reels vertical (1080×1920)
- Answer image — landscape (X)
- Answer image — square (Instagram)
- Answer image — vertical (Shorts)
- Post drafts (JSON)
Free to use for non-commercial purposes such as classes, school projects and blogs, with a link back to this page as the credit. Commercial use is not covered
Every figure is generated here from the phenomenon itself (re-implemented). The general Ponzo illusion principle is re-implemented here as SVG. No existing figure or code is reproduced.