ONE of the most identifiable features of the Yorkshire Dales and North York Moors is the dry stone wall that is as synonymous with the landscape as the sheep it is built to contain.

It’s amazing to think that some of these walls have been around for hundreds of years, built so sturdily that they still do the job as well they did when they were first constructed, despite the fact they have nothing but gravity, friction and the skill of the builder to hold them up. Part of their longevity is down to the fact that they move and give when battered by the elements, with rain, wind and snow able to pass through as well as around them.

There is evidence to suggest that Britons were building dry stone walls since before Roman times, often as a way of keeping predators away from settlements. Some early examples in the Yorkshire Dales have distinct overhanging top stones which it is believed were designed to stop wolves leaping over them because the design died out at the same time as wolves became extinct at the end of the 15th century.

It was during the medieval period, as people moved to live on higher ground, that they became very popular. The higher you lived, the fewer the trees that grew there, and therefore less wood was available to build a structure to contain your livestock. But stones were plentiful, even though it was a laborious and backbreaking process, digging the rock out of the ground then transporting it by cart or sledge to wherever it was needed.

Medieval monks also favoured the technique during the construction of their churches and abbeys, and fine examples can be seen at Fountains Abbey near Ripon.

As the feudal system in England died out, common land was divided up during the period of enclosure in the 18th and 19th centuries and private owners became responsible for their own parcel of land, which in upland areas was marked out by dry stone walls.

As my dad mentions in his column from February 28, 1981, the strength of the wall depends on it having good foundations and correctly-placed "through" stones. A through stone is a larger piece that spans the full width of the wall and is paced at regular intervals along and up and down the wall. It keeps smaller stones below it place, and increases the stability above it.

The shape of the wall is like the letter A, wider at the bottom then gradually narrowing towards the top. Stones are sorted into sizes, with those that will make suitable through stones set aside. A channel, slightly wider than the wall, is first dug out of the ground, up to a foot deep, and the largest stones are placed in it for foundations, with small stones filing the gaps. A skilled craftsman will know which shaped stones should go where, where to put those with curved edges, and where to put those with more angular shapes. Once it is built, it is often finished with a tightly packed row of stones placed vertically with curved edges pointing up.

The whole lot will then stand for many, many years, without any need for cement or mortar, with simply gravity and the weight of the stones themselves holding it all in place. They become a rich habitat for a whole host of flora and fauna, with creatures like field mice, shrews, hedgehogs and insects using them for shelter, while birds will nest in them, and hunters will perch atop to spy for prey.

They also support various species of moss, lichen and wildflower, each one flourishing in its own mini ecosystem that evolves on the part of the wall that suits them. Some will be found on the cooler, windy, wet, north face of a wall, while others will enjoy a warmer, drier, south facing side.

In North Yorkshire we have 13,000 miles of dry stone wall, while nationally there are almost 120,000 miles. Unfortunately, only a relatively low percentage,13 per cent, are in good condition, with 17 per cent in a state of advance decay. A whopping 70 per cent are considered derelict.

Thankfully, there are still skilled craftsmen out there continuing to pass on their art, teaching others how to build with courses, video tutorials, and workshops, helping to preserve and maintain this wonderful feature of our historical landscape.

Contact me, and read more, at countrymansdaughter.com. Follow me on Twitter @countrymansdaug