That wall is about 50 years older than the house and extends from the street at the front right to the back of the garden and beyond. So it would have been built around 1780 and the indications from a very old and badly defined map I found in the library some years ago showed that it probably enclosed a large tin mine of which further records are non-existant. A survey report did reveal adits below the house but as the closest one to the surface is 50 feet down and the rock is granite there is no possibility of land slip, even if St Day is known as 'Sinking City' (as fields and occasionaly houses have disappeared into sudden and unknown - or perhaps more usually - unrecorded mine shafts opening up especially in very wet weather and of which the mine caps were not durable enough, especially over the course of centuries!).