What literary term is illustrated in this sentence But when they had now reached the mid assembly place of many voices there wheeled about and flapped their strong wings?

The sentence you provided illustrates several literary terms, but the most prominent one is alliteration.

Here's why:

* Alliteration is the repetition of consonant sounds at the beginning of words that are close together. In this sentence, we have:

* "w" sound in "wheeled" and "wings"

* "f" sound in "flapped" and "strong"

This repetition creates a rhythmic effect and draws attention to the action of the birds.

It's also worth noting that the sentence uses imagery to create a vivid picture of the birds' movement, and possibly onomatopoeia if the word "flapped" is meant to sound like the actual wings.