description of the peel tower. Why had it-been built? Why had it fallen into disuse ?

The Peel tower looked "empty and forlorn as a hollow tree". "Peel" was a term used for the towers or strongholds that the wealthier people in England live in. These "peel-towers" gave them better protections from raiding Scots. There had been no raids for a long time hence the disuse.

We got the idea of a stronghold from the old peel- tower which stood some way down the valley. In grandfather's time, all the wealthier people lived in peel towers of that kind, because you never knew when the Scots might come pouring over the Border on one of their raiding expeditions. But there had been no such raids since I was born, and some of the local squires were giving up their "peels" and building ordinary houses.