Question: Who was the reigning king when the Builth Castle was built and who was also known as "Malleus Scotorum"?
Sentence (from "Edward I of England"): Edward I (17/18 June 1239 – 7 July 1307), also known as Edward Longshanks and the Hammer of the Scots (Latin: "Malleus Scotorum" ), was King of England from 1272 to 1307.
Relevant evidence: Yes