Gabions (from Italian gabbione meaning "big cage"; from Italian gabbia and Latin cavea meaning "cage") are cages, cylinders, or boxes filled with rocks, concrete or sometimes sand and soil that are used in civil engineering, road building, and military applications. For erosion control caged riprap is used. For dams or foundation construction, cylindrical metal structures are used. In a military context, earth or sand-filled gabions are used to protect artillery crews from enemy fire.

Leonardo da Vinci designed a type of gabion called a Corbeille Leonard ("Leonard[o] basket") for the foundations of the San Marco Castle in Milan.

In civil engineering a gabion wall is a retaining wall made of rectangular containers (baskets) fabricated of thick galvanized wire, which are filled with stone and stacked on one another, usually in tiers that step back with the slope rather than vertically.

The most common civil engineering use of gabions is to stabilize shorelines or slopes against erosion. Other uses include retaining walls, temporary floodwalls, to filter silt from runoff, for small or temporary/permanent dams, river training, channel lining. They may be used to direct the force of a flow of flood water around a vulnerable structure. Gabions are also used as fish barriers on small streams.