The Boston Marathon , which had been run since 1897 , was rocked Monday by two explosions at the finish line . The Marathon has been held since 1973 . In all , 26,839 runners and wheelchair users registered . There are participants from 56 U.S. states and territories .
The Marathon has been held since 1973 . In all , 26,839 runners and wheelchair users registered . There are participants from 56 U.S. states and territories .