I'm partial to Mozart's operas, though I have very little music theory or history foundation to speak of. A few days ago I was idly pondering how far apart the standard voice ranges are - for instance, tenor and mezzo-soprano. Wikipedia to the rescue! There is a lovely chart comparing not only human voice ranges, but also a number of instruments. The answer to my query - they overlap by about one and a half octaves.
In the same article, I was amused to see the note about highest and lowest notes in standard singing repertoire - both are in Mozart operas! The highest is in both arias sung by the Queen of the Night in Die Zauberflöte, and the lowest is sung by Osmin in Die Entführung aus dem Serail. So, not only Mozart operas, but specifically German Mozart operas.