Isometric help

[haunter]

Ok, here is an image i've been using to tryout some isometric graphics... Just basic shapes so far... Now, I want you to ignore all of the shapes except for the archway... I can't seem to get the curves to look right... For example, on the outside curve, the two curved lines don't look like they match... So right now I'm just looking for help on drawing curved objects in an isometric perspective... Any tips or whatever?