Cantonese is ancient as well as modern
As spoken today, Cantonese features certain phonological characteristics that are quite close to some pronunciations in Middle Chinese. In fact, some classic Chinese literary pieces, especially poetry, sound close to the original when read in Cantonese because Cantonese phonology is similar in many aspects to the pronunciations used in Middle Chinese.
In contrast, the pronunciation of Mandarin is very different from Middle Chinese; thus, poetry in Middle Chinese can sound quite discordant when read in Mandarin. Using Mandarin phonology in poetry and other rhyme-based writings originally composed in Middle Chinese may sometimes make the lines of the poem sound quite incoherent as Mandarin differs so markedly from Middle Chinese phonology.
