Netherlands - ? about a'dam for anyone who lives there

[abraham]

Swim is just curious about the last time he visited a'dam. This was about 5 or 6 years ago now, but swim remembers later on at night, not sure when but probably 10 or 12 at night, a bunch of cops(Swim assumes) came out on the streets with motorcycles (enduro type dirt bikes) driving all over the place and the streets seemed to empty. This was not all to late and swim and friends wondered what was going on. Is there some kind of curfew? Or what was the deal. The streets just seemed to quiet down fast and fairely early. Just curious. thanks for any input.