Why are some window bars curved at the bottom?

While walking through an old neighborhood or looking up at a building in the city center, you may have noticed these window grilles that are slightly curved outwards. A rounded shape, almost like a small metal "belly". Decoration? An architect's whim? Not at all. These discreet curves actually hide an idea that is as practical as it is clever.

Not-so-ordinary window bars

Safety bars have been around for centuries. Their main mission is simple: to protect homes by reinforcing openings, which are often considered vulnerable points.

But over time, the strictly straight lines gave way to more elaborate shapes. Among them, the outward-curved model — sometimes called the "belly bar" — which owes nothing to chance.

What is this curved "belly" for?

Contrary to what you might think, this shape is not only aesthetic. It provides extra space outside the window, without encroaching on the interior of the room.

In urban environments where every inch counts, this space becomes particularly valuable.

• An ideal stand for planters

This is undoubtedly the most visible and charming custom.

The curvature creates a natural niche where planters can be placed stably. Colourful flowers, aromatic herbs or hanging plants can thus find their place without the risk of falling, provided that the planters are adapted to the width of the grid and correctly propped up.

The result?

Lively and flowery facades that transform an ordinary street into a postcard-worthy setting. In many European cities, these domed grilles are an integral part of the architectural charm.