Our Greek Myth party invitations were extremely simple.
Not being able to find good clip art for Greek Myths, I stuck with simple columns to frame the page.
The columns help conjure images of Greek temples. I used the font Castellar, but I'm sure there are more ancient- Greek-looking fonts out there on the web.
The invitations read:
Come Celebrate _____'s Birthday With Us
We're going to party like it's 500 B.C.
If you can come 'in character', please do.
Consult the Oracle (enclosed) to learn your destiny.
Included in each envelope was a smaller envelope, marked "THE ORACLE".
Inside each Oracle envelope was a brief description and picture of a Greek god.
We assigned each guest a different Greek god. My son, of course, wanted to be Poseidon (who figures prominently in the Percy Jackson books).
So far, the invitations have been a hit and most guests have replied that they will come in costume!
There are a few other blogs on the web that describe Greek Mythology parties (or Percy Jackson parties).
Here are some that I used for inspiration:
Small Hours and Little Wonders for a detailed Percy Jackson party with lots of game ideas
Bright Hub for generic Percy Jackson ideas
eHow for generic ideas for a Greek Myth party
Make It Do for a detailed description of a Percy Jackson party (great cake picture!)