The Peel of Buchanan

In a previous posting I referred to my search for "the old Buchanan castle". I had seen various references to this building, which existed in the 1600s and probably much earlier. It seemed  that it had to refer to the old manor house "Buchanan Auld House". But this seemed to be a "mansion" rather than a "castle". So where does the term "castle" come in? Finally I found references to the "Peel of Buchanan" which stood not far from the Auld House. A "peel" was a "tower house", a small castle resembling the "keep" of a large castle, but smaller, typically 4 or 5 stories high. From this description in the History of Stirlingshire, the Peel of Buchanan was definitely a castle, complete with a moat, and probably a drawbridge.

'We may now pass to another remarkable antiquity, which, like the last mentioned, has, hitherto, so far as is known, been unnoticed in print—" the Peel of Buchanan," about 200 paces in front of the mansion of His Grace the Duke of Montrose. The Enric [river] had had its course in this direction, though now flowing considerably to the southward. The ditch around this ancient fort was filled by the river, and crossed by a passage, probably a draw-bridge, from the north.'
The History of Stirlingshire, Volume 1, By William Nimmo, Robert Gillespie, page 59, published 1880