On a Friday morning, people walking on the Brooklyn Bridge solemnly made way for a group of 50 firefighters marching from Ground Zero to the Co-Cathedral of St. Joseph in Prospect Heights, where they celebrated a Mass for those lost on Sept. 11, 2001. The firefighters were carrying 23 flags, one for each of the members of Battalion 57 who perished trying to save lives after the attack on the World Trade Center.