Then Buchan could easily have copped this theme straight from Phèdre, but why he would attribute this gruesome deed to the actual Erskines, I don't know.

In the Chanson de Roland, the traitor, Ganelon, is tied in that exact fashion to four stallions (as almost all warhorses were, at the time), who were set loose in a field of mares. Even normally well-behaved horses can become chaotic under such circumstances. Again, I wonder if Mr.Buchan was a fancier of French literature.