Transparent half circle cut out of a div

Question

I would like to make a transparent cut out half circle shape using only CSS3. The only requirement is that all the elements that form the shape must

Answer 1

Right now, the only way I can think of would be to use a lot of 1-pixel wide black divs next to eachother with varying height. It's technically possible this way but should be deeply frowned upon. Also; you won't have anti-aliassing unless you want to go through the trouble of adding 1x1 pixel divs and do the anti-aliassing manually.

It might be more helpful if you gave an example of how you wanted to use this. Why does it need to be black/transparent only? As stated by omarello, the best solution on most circumstances is probably a simple GIF or PNG image with transparency.