I've been watching this small farmhouse slowly disintegrate over the past 45 years. When I first knew it, it was just an abandoned isolated ruined house with attached barn, pigsties, and other small outbuildings. Then the roof gave-in. Today there is very little left.
I recently noticed another newly collapsed wall, and saw that it was the perfect illustration for how these houses were originally built.
The stones came either from the fields, or from a nearby communal village quarry. The 'mortar' was no more than earth, and the trees for the roof structure, etc, came from the surrounding woods. The roof tiles must have been the main expense, as they needed to be purchased.
All that was then needed was a piece of string with an attached pebble (plumb-line), a few tools, and a level.
They may sound flimsy, but as long as the walls were kept dry (a good roof), they remained solid for centuries. Just stones, earth, and wood. Our house is built like this, and it's lasted 300 years so far.