Ah, you're onto the unpatriotic part, eh? Killing off the English army single-handedly.
The portal you're seeing on the map is the entrance to the area that disappears as soon as you enter Barcelona. The portal you're looking for is in the Crossroads, so you have a bit more figthing to do yet.
AFAIK, the goal is just to get to that portal, it doesn't matter how many soldiers you kill (though the more the better for the extra XP gained).