Wednesday search challenge (1/23/13): What, why, where are these stone circles?

I was walking the other day and came across part of a fragment of a stone circle embedded in the street. That was odd, but I didn’t think much of it until a little while later I happened to come across a full circle, also laid perfectly in the street, made entirely of bricks. Once is odd, but twice makes me pay attention.

When it happened a THIRD time, I started wondering why the city would be making such interesting marks on the pavement.  Is this the rise of a new Stonehenge culture?  Could it be the mason’s version of crop circles?  Maybe they're secret ICBM missile silos! Today’s challenge:  What are these circles?   Why and when were they made?  How many more can I expect to find?  Finally, in what city do these circles appear?

As always, please let us know what the answer is, and most importantly, HOW YOU SOLVED the challenge!  If you’d include a time estimate on how long it took, that would be great too.
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