Mary Norris writes about the meanings and usage of semicolons, always a fascinating topic, in The New Yorker:
So the semicolon is exactly what it looks like: a subtle hybrid of colon and comma. Actually, in ancient Greek, the same symbol was used to indicate a question.
And it still seems to have a vestigial interrogative quality to it, a cue to the reader that the writer is not finished yet; she is holding her breath.
If you find this to be the least bit interesting (which is not a given, I admit), be sure not to miss Ben Dolnick’s article in The New York Times that Norris refers to at the outset: “Semicolons: A Love Story”.