Editions of works in the original languages are classified under call number PA, with occasional exceptions.
Translations of classical literary works (e.g. poetry, drama) are usually have call numbers beginning with PA
Translations into English of "nonliterary' works, such as history, philosophy, and geography are usually classified according to their subject matter (e.g. Greek History: DF; Roman History: DG; Philosophy B). Classifications of commentaries and secondary literature on such works is less consistent.
To find translations of works by Greek and Roman writers use the specific search feature of the library catalog.
Enter the author's name in the author box. Usually, this will be the common anglicized form of the name: e.g Cicero, Livy, Aeschylus etc and search. Then click on language in the refine search options on the right and select English (or another language you can read.)
The Perseus Digital Library provides online translations of many ancient authors and much more. In general these are older translations, however, and you will better off using a more recent print edition of the text in question.