"We stand on the bridge and no one may pass"?? Oh please! Is this homage or ripoff?
That is a reference (in both Tolkein and B5) to at least two heroic "stands" on bridges
1) That of Horatius in ancient Rome, who single-handedly held the last bridge into the city against a barbarian force until other would weaken the supports and collapse it. (Horatius survived by diving into the Tiber and swimming to the Roman shore.) This incident may be history or legend, but it is certainly well known and often cited in literature. (And elsewhere. In Blue Thunder a reporter says, "This may be the biggest story since Horatius at the bridge" - a reference that must have gone over the heads of 90% of the people in the theater.
2) The second one I'm less clear on, though I suspect it was Tolkein's primary inspiration (since he had a great interest in Scandanavia and the Viking settlement of northern England.) In 1066, just prior to William the Conqueror's landing at Hastings, England was invaded by the Norman's Norse cousins. King Harald had to move a force north to intercept them. In the course of the battle there was another instance of a single warrior holding off an entire enemy force by himself on a narrow bridge. (But I can't for the life of me remember which side he was fighting for.) His fate was rather less pleasant, as an enemy soldier was able to wade out under the bridge undetected and shove a spear up through the slats of the bridge, stabbing the heroic fighter in the groin. (Ouch!) He collapsed and was swiftly killed.
Regards,
Joe
Lol! 
