Premise: Horsburgh Castle, also known as Horsbrugh Castle or Horsbrugh Tower, is a ruined tower house castle by the River Tweed, on the A72 road from Peebles to Galashiels, near Glentress in the Scottish Borders area of Scotland. The ruins date from the 16th century and was built by the Horsburghs.
Hypothesis: The builders of the castle are unknown.