The big day has finally arrived for Taylor Swift and Travis Kelce ... and they've transformed Madison Square Garden into their private love compound.

Check out the pics ... even into the night, the place was surrounded by police and other security measures.

It makes sense ... as TMZ reported, the star power there last night for what we believe to be the rehearsal dinner was massive -- and there's going to be even more today for the wedding bash!

TMZ broke the story ... more than 70 detectives from precincts all across the city are assigned to Thursday's rehearsal and Friday's wedding ... and they'll be working 8.5-hour shifts at $80 to $90 an hour. We'll spare you the math ... that's $95,200 on the low end.

In addition, we're told there will be over 50 police officers assigned to MSG as well ... they're mostly rookies making $70 an hour for a 9-hour shift ... which would be another $63,000.

Our sources say some NYPD higher-ups will also be working ... so the salary figure should push over $160K.

But hey, you can't be too, too careful when the biggest stars on the planet gather for a party!