The craft of dry walling, which means building in stone without mortar or cement, must be very old. How old we do not know. The prehistoric drystone builders could assemble a roof in the shape of a set of long stones, on very narrow chambers. Before the advent of mortar, they employed their skills to erect mausoleums and open air temples. Later as agriculture and animal husbandry developed, so did work in dry stone. Dry stone features such as ramps and terraced retaining walls made food production sustainable in hilly and mountainous areas. Freestanding dry stone walls were - and still are built high enough to be termed "stockproof"  - and served to protect the livestock from predators as well.  A dry stone retaining wall is built in the same fashion as a freestanding wall. Structural features such as a protruding foundation, proper filling, tie stones and capitals will fortify and extend the life of the consrtuction. Built to stand on its own - it is backfilled and compacted behind during construction. Well built, the wall will need little maintenance over its life and will serve for centuries.