How did a Balrog get beneath Moria and when?

[Cirdan]

Originally Posted by Galin

Still it might be noted that this was written when Tolkien imagined (seemingly) thousands of Balrogath at Morgoth's command in the First Age; and there is at least one later indication that Tolkien was considering a quite drastic reduction in numbers (at most seven)!

Tolkien never really got around to a true rewrite of the end of Quenta Silmarillion
-- outside of some cursory corrections, concerning which Christopher Tolkien warns do not necessarily illustrate that this section of QS thus was fully 'updated' and revised by his father.

Would JRRT have revised 'few' if he went ahead with this reduction? I don't know, but I'm just saying this line really hails from the late 1930s, well before Tolkien at least mused about reducing Balrog numbers in Middle-earth.

The quote from Letters that I had just offered above would seem to confirm this idea -well, that there was (perhaps) only one left. Do you have something you can quote for us here from the War of the Jewels History volume, or is this idea that there were supposed to be only a few Balrogs from another source?