However, this system isn't appropriate for citations of ancient texts. There are a gazillion different translations and editions of Plato's Republic, for instance, so referring to a page number from the translation you're using would make it very difficult for others to track down the passage.
Because of this, more-or-less standards system of reference have developed for many ancient authors, to facilitate finding passages across differing editions and translations. Please use these systems in your paper.
For Aristotle, use the Bekker numbers, e.g., "Blah blah blah." (Nicomachean Ethics 1173a10-15)
The situation with Hellenistic philosophers (the Epicureans, Stoics, and Skeptics) is a little trickier, as we have a huge range of sources of information to contend with. However, for our purposes, most of our references will be in passages in one of the widely-used compendia: either Long and Sedley, or Inwood and Gerson (The Epicurus Reader or Hellenistic Philosophy: Introductory Readings). Please piggyback on their way of referring to the primary texts, e.g., for text 2 of The Epicurus Reader, go ahead and do the following: "Blah Blah Blah." (Letter to Herodotus 82), and for text 29, "Yadda yadda yadda." (Plutarch, Against Colotes 1111a). You may also wish to include the 'number' of the text as used in your compendium. The following convention would work: (IG [text number]) for Inwood and Gerson, (LS [text number]) for Long and Sedley, e.g., (Plutarch, Against Colotes 1111a, IG 29).
For references to Lucretius, the most common reference system is (DRN [for 'De Rerum Natura,' the poem's title] Book-number line-numbers); e.g. (DRN IV 1121-1140).
Unless you are doing your own translations, please indicate in a footnote which translation you'll be using, e.g., "All translations of Lucretius are from Smith (2001)."
For most of the sources above, it might occasionally be difficult (using your translations and their marginal numbers) to pinpoint exact line or section numbers: did that quotation from Plato end at 460d or 460e? If you were writing a journal article, you'd have to go back to the Greek or Latin text and pin it down exactly, but for our purposes, don't sweat it.
If you are referring to other ancient sources that aren't covered in the guidelines above, please feel to ask me if there is some widely-adopted convention that you should follow.
Send e-mail to tokeefe AT gsu DOT edu