Why do some window grilles have a curve at the bottom?

Window bars, also known as security bars, have been used for centuries as an effective barrier against theft and unauthorized access. Beyond their protective function, some grilles feature an outwardly curved design at the bottom, commonly called the “grandmother’s belly” or “donkey’s belly” style. But why this particular detail?
Functionality and design in a single element

This type of curve is not only an aesthetic issue. It has several practical advantages that make many homeowners opt for this design:

Greater usable space: The curvature creates extra space between the window and the grille, ideal for placing flower pots, aromatic plants or even portable air conditioning units without compromising safety.
Better ventilation and light entry: By moving the grilles away from the window frame, you allow for better air circulation and a freer entry of natural light, which is especially useful in hot climates.
Aesthetics and added value: This type of design brings a classic or artisanal touch to the façade, raising the visual appeal of the home and, in some cases, even its commercial value.
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