Definition of "morion"

The Roman footmen caried not their morions, sword and target only, as for other armes (saith Cicero) they were so accustomed to weare them continually, that they hindered them no more than their limbs […].

1603, Michel de Montaigne, chapter 9, in John Florio, transl., The Essayes […], book II, London: […] Val[entine] Simmes for Edward Blount […]

This unlucky defect, however, his industry supplied by a vizor, which he made of paste-board, and fixed so artificially to the morrion, that it looked like an intire helmet.

1755, Miguel de Cervantes, translated by Tobias Smollett, Don Quixote, Volume 1, I.1

The morion is a kind of open helmet, without visor or bever, somewhat resembling a hat; it was commonly worn by the harqubussiers and musqueteers.

1786, Francis Grose, A Treatise on Ancient Armour and Weapons, page 12