The characteristics of the classic bastle house are extremely thick stone walls (1 meter or so), with the ground floor devoted to stable-space for the most valuable animals, and usually a stone vault between it and the first floor. The family's living quarters were on the floor above the ground, and during the times prior to the suppression of the reivers, were only reachable by a ladder which was pulled up from the inside at night. The only windows were narrow arrow slits. The roofs were usually made of stone slate to improve the bastle's fire-resistance.
Bastle houses have many characteristics in common with military blockhouses, the main difference being that a bastle was intended primarily as a family dwelling, instead of a pure fortification.
Many bastle houses survive today; their construction ensured that they would last a very long time. They may be seen on both sides of the Anglo-Scottish Border.