Indeed the Romans had a big part in world (and especially European) history, but nevertheless it's not my duty or I even would say, it isn't belonging to common knowledge, to know, what the Arch of Constantine was or even is. It is sufficient to know the Arc de Triomphe, if you know "the original" you get 100 points more on your score.
Other things about the Roman Empire are more important to know than this thing.
(btw: Last year I went to Rome with my history class and we even saw the Arco di Constantino, but it wasn't even mentioned by our tourist guides or history teachers. Therefore we know more things about the Colosseo or Ostia or a few other things, that are more important and related to Rome)