Should you wish to cite ancient historian who happened to have written in Greek... First you'd look for a decent translation (because it'll search more comfortable if you can immmediately see what it means ) next you could try and see if you got acces to the Thesaurus Linguae Graecae. (TLG for short.) From there you can try to read the source in its original language to make sure your translation is correct. (For instance the whole stirrup controversy (hint: 1898, 1962) seems to have originated mainly from how certain 'Frankish' words were interpreted (wrongly) and the conclusions drawn from them.)

If that doesn't work: you can try this too... http://www.fh-augsburg.de/~harsch/augustana.html