The Hebrew Bible mentions left-handed people on three occasions: the story of Ehud’s assassination of the Moabite king (Judges 3:12–30), the 700 Benjamites who could use the sling with deadly accuracy (Judges 20:16) and the two-dozen ambidextrous warriors who came to support David in Hebron (1 Chronicles 12:2). All of these stories of left-handed people in the Bible appear in military contexts, and, curiously, all involve members of the tribe of Benjamin.As usual, this essay is an (interesting) summary of a BAR article that is behind the subscription wall: Boyd Seevers and Joanna Klein, Biblical Views: “Left-Handed Sons of Right-Handers,” from 2013.
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In Ferniehirst Castle in Scotland there is a left-handed (i.e., upwards counter-clockwise) spiral staircase. The story is that in the early 1500s Sir Andrew Kerr had it built because he himself was left-handed and he trained his follows to swordfight left-handed. The layout of the staircase made it easier for them to defend the castle entrance from above. I have found mixed views on whether it would have made an attack from below harder or easier for right-handers.
There is also mixed evidence on whether left-handedness ran in the Kerr Clan. It doesn't seem to today.
I have seen the staircase myself, but I don't know how much else of the story is true. For some commentary and links, see here.
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