.. How do I solve this puzzle with the letters and symbols?

When you enter the Judges area of the Underworld, take a step toward the blue doors, then turn right and go up the steps. At the top of the stairs, there's a small pillar with Greek letters and symbols in a circle. You can't do anything with it until you break into the "Personal Notes" section of Grigor's tablet --

How do I get into Grigor's tablet?

-- see a note titled "Don't shoot the messenger" (not "Seriously, please don't shoot the messenger," which is a different note) --

-- and get the rubbings of the Greek alphabet from those green panels.

What do I do with these green plates with partial letters?

What you're trying to do here is move the round pieces to the correct slots. Read to the end of this hint for a picture showing which tile goes where and a step-by-step to get them there.

You'll need to figure out which five famous Greeks are being referred to, what they're famous for, and what color each one gets.

Grigor's note is very helpful at this stage. He says the doctor is red, the playwright is orange, the architect is green, the inventor is blue, and the poet (who is female) is purple.

There's one letter in each color, so now you know the letters: the red chi is the doctor, the orange epsilon is the playwright, the green phi is the architect, the blue alpha is the inventor, and the purple sigma is the female poet.

(If you care, the book on famous Greeks will tell you that the doctor is Hippocrates, the playwright is Euripides, the architect is Phidias, the inventor is Archimedes, and the poet is Sappho. But you don't really need to know this.)

It's not too hard to pair up the symbols with the people. The doctor gets the caduceus (the snakes on the winged cross), the playwright gets the drama mask, the architect gets the temple, the inventor gets the diagonal corkscrew (which is actually a brilliant little invention called an Archimedes screw), and the poet gets the scroll-like piece of paper.

Now on to the more irritating part. You're trying to move the letters to the places that are the proper color for them and that also have the little blue and white dots on them. The symbol that goes with that letter goes to the place with the same color but no blue dot.

So, for example, the doctor's chi should end up at the red slot with a dot in the lower right, while the caduceus belongs in the red slot at the upper left.

The center slot and the inner slots will be empty at the end; they're just temporary spots to use while you shift the pieces around.

Any way you do this is the right way. Have fun. But if you dislike this kind of puzzle as much as I do (will someone hand me a crowbar and a hammer, please?), here's the step by step.

Famous Greeks Puzzle, Amateur

Famous Greeks Puzzle, Master

As to what the stuff you find here is for, the piece of paper will help you with one of the puzzles in the endgame --

How do I get the thing Grigor left for me?

-- and the other is evidence of how the thefts were accomplished, though it's not enough to convict. Keep gathering info!