HAve you been in a coma or what?? It's the Ist April everywhere else. Perhaps you should see a shrink Jimi- timeslip is a serious and dangerous delusion ( though not as bad as ringslip)
In 1572 that was..... Holland was at war with Spain. Actually, we allowed them to stay for a while (for as long as close to 100 years) but at the end of March in 1572 they started to become a nuicance. So, on the 1st of April we (that's mostly organised Pirats) kicked them out of Brielle (that's where I live). Afterwards other Dutch towns and cities start doing the same and thus the victory of the famous 80-years of war with Spain, started in Brielle.
Nowaday Brielle isn't wurth much, especially not (!!!) for tourist, so don't come by and certainly do not stop. It's nice and quite and we like to keep it that way.....
Oh, each and every year or the 1st of April we get a bit over-excited while celebrating the old historic moment. Nevertheless, this is of no interest at all for outsiders so b*gger off....