It all started with a simple song...and turned into a giant flash mob.
The group descended upon Copley Place, which is about a block from the bombing site.
It began as a Valentine's Day surprise from Jessica Downes for her husband, Patrick. Both lost their legs in the attack.
Everyone said the event brought them together and helped them heal -- and it became a surprise Valentine for the entire city of Boston.
To see their surprise unfold, watch the video player above.
For much more on this story, click here.