In his Lives (1827), Peter Walker recounts a baffling spectacle seen on Scotland’s River Clyde in the summer of 1686:

[T]here were showers of bonnets, hats, guns, and swords, which covered the trees and the ground; companies of men in arms marching in order upon the water-side; companies meeting companies, going all through other, and then all falling to the ground and disappearing: other companies immediately appeared, marching the same way.

Walker says these reports continued for at least three afternoons, but notes that fully a third of the assembled crowd, including himself, could see nothing. That sounds like a mass delusion, but “those who did see, told what works (i.e. locks) the guns had, and their lengths and wideness, and what handles the swords had … and the closing knots of the bonnets.” Make up your own mind.