Michel de Montaigne

“ It was at Rome a signification of favour to depress and turn in the
thumbs:
"Fautor utroque tuum laudabit pollice ludum:"
["Thy patron will applaud thy sport with both thumbs"
—Horace.]
and of disfavour to elevate and thrust them outward:
"Converso pollice vulgi,
Quemlibet occidunt populariter."
["The populace, with inverted thumbs, kill all that
come before them."—Juvenal, iii. 36]
The Romans exempted from war all such as were maimed in the thumbs, as
having no more sufficient strength to hold their weapons. ”