# Decrease in filter size as CNN progresses?

I have noticed, as a trend, people seem to "taper" the size of their filters as a convolutional network progresses. By this I mean they begin convolving the image/patch with a larger filter, and slowly decrease the size each layer until the output.

I have also employed this approach and had very good results, however I am not sure why.

Is there a reason this should be done, or is it just "black magic"?

Thanks!