The donjon was intended as a residence capable of being defended by a small garrison, in case the remainder of the castle fell into enemy hands.
Before being partially destroyed in 1337, it was 20m in diameter with walls 4.6m thick.
The picture shows the original side, that is, the one which has not been re-built.
The castle has been described as
the grandest piece of secular architecture that the Middle Ages have bequeathed to us in Scotland.
by whom, the leaflet does not say.