Was the chiasma common in Latin? Or an uncommon figure of speech?
(Words in a sentence with the pattern ABBA or ABBCBBA, etc...)
Where could we meet the greatest amount of chiasma? In poetry? In speech? In prose?
How was it used? To put an emphasis or something? What was its role in stylistic?
Which words were more commonly use as the "C" in my AB-C-BA example? A particular type of word?
Chiasms are mostly used in poetry and high rhetoric, for dramatic or or playful effect. What they do is emphasise the words that seem inverted, draw the reader or listener's attention. I would say the frequency and effect of chiasms were not so different from how they are used in the modern languages. I think the 'C' in ABCBA could be anything; it depends entirely on the sentence. Typically a word like et. I suspect ABBCBBA would be very rare; you don't happen to have an example available?