Gabions are best thought of as large, wire baskets that are filled with a local stone and linked together to form terracing, retain river banks, support earth banks and limitless other uses in the civil engineering field.
The 'baskets' come in a variety of dimensions, generally 1m wide x 1m deep x 1-4m long, and a selection of mesh sizes to suit the various applications. and by using local random stone, generally in chunks 100-200mm, and being very simple to install, the cost is kept to a mnimum, and the finished result is aesthetically pleasing.