Legion adjectives are listed in this post. Each word below can often be found in front of the noun legion in the same sentence. This reference page can help answer the question what are some adjectives commonly used for describing LEGION.
american, british, entire, fifth, first
foreign, fourth, german, hellish, italian
new, ninth, own, roman, same
second, seventh, single, sixth, tenth
theban, third, twelfth, whole
Hope this word list had the adjective used with legion you were looking for. Additional describing words / adjectives that describe / adjectives of various nouns can be found in the other pages on this website.