For centuries, throughout the world, agricultural walls and fences were made to keep both wild and domesticated animals out of certain areas, such as gardens or crop fields.
Early fences were made from whatever material was available to hand, whether that was stone, timber or earth.
On more rugged and hilly areas where the grassed areas were littered with stones, during ploughing or sowing times these were removed to the edges of the crop field. Over time, these piles became the walls of the fields. In the UK especially, how the stone walls are constructed very much defines the location, Yorkshire dry stone walls and Cornish 'hedges' being two well-known examples.
Where wood was plentiful, splitting logs and forcing them vertically into the ground and connecting these posts with rails was a cheap and effective method of creating a barrier. Other types of wood fences could be made from weaving hazel or willow into panels.
An earth barrier, or 'ha-ha', was constructed by digging a ditch with one steep side, which animals couldn't clamber up, and one gentle slope.
Farm Gate origins
Over time, with the increase in pastoral farming, the emphasis on fencing changed to farmers having to keep their animals contained, and so the need for gates arose. The word gate is derived from the old Norse "gat", meaning path or road, where the 'gate' was actually the gap in the wall or fence, not the barrier itself.
Railway fencing
With the increase in the numbers of Acts of Parliaments allowing Railways to be built, the various Regulation of Railways Acts required railways to be fenced. The original statutory requirement was for them to be fenced against trespass from the railway onto the surrounding land, and to keep animals off.
As the number of roads and railways grew, it was also necessary to provide controlled access points, both across the thoroughfares and into dedicated yards. Gates were traditionally made from wood - it was cheap, plentiful and easily worked, and provide a stout but movable continuation of the adjoining fence or wall. As with the walls and fences, gates became synonymous with the areas in which they were used, and also for the specific use they were put to.
More modern gates are made from iron, steel or aluminium. These should last longer, but seem to be more prone to being damaged, and the iron or steel versions often go very rusty.
The Country Code
In rural parts of the UK, the Country Code recommends leaving farm gates you pass through as you find them - either open, or closed. Open gates allow livestock to access water supplies, vital in warm or hot weather.