At UW Seattle, they bricked over Red Sqare (and hence made it red) so that they could use water cannons on the protesters and they'd have nothing to firmly attach/affix themselves to, whether that be trees, stakes in the ground, etc. This was also done to many urban spaces and college campus squares at the same time, as it is very effective.

Note: love the downvotes, keep 'em coming. I'm just referencing history here :P