Although they are not to everyone's taste, gabion walls can look amazing and they tick quite a few sustainability boxes. Relying only on passive weight to do the work of retaining, they require no concrete footings. Production of cement requires intense heat which contributes to global CO2 emissions. Old waste concrete can be broken up and used in the body of the wall behind the facing rocks instead of going into landfill. They are also naturally free-draining, eliminating the need for additional plumbing work.