broch

noun1

1. •
   A type of Iron Age stone tower with hollow double-layered walls found on Orkney, Shetland, in the Hebrides and parts of the Scottish mainland.

   • Finella's carles builded the Kaimes, a long line of battlements under the hills, midway a tower that was older still, a broch from the days of the Pictish men […]. — 1933