Walls of
Gondolin: historically, as described by Herodotus, Ecbatana, the modern Hamadan, the Persian capital, was surrounded by seven walls. This is quite possibly
Tolkien’s inspiration.
The gates (of necessity) duplicate this number and should not count as a separate seven. But there are only six tunnels, not seven, as the lowest level of the
city has no tunnel.
Of course the Thebes of Greek legend was also famous for its seven gates, though they were all in the outer wall.
The stars of
Durin composing Durin’s crown and the Valacirca are the same thing, and the Valacirca has seven stars because in fact the Great Dipper in reality has seven stars.
Dwarvish Rings of course connect, finally, with Dwarvish clans, though admittedly created as a group of seven before the idea of giving them to
Dwarves emerge.
Dwarf hoardes and Dwarf fathers duplicate the clans and Rings and are not separate sevens.
The seven Durins may symbolically reflect the seven Dwarf clans also.
(I wonder if the story “Snow White and the Seven Dwarfs” was an unconscious influence on Tolkien’s persistant use of seven for his Dwarves.)
The seven stars of the rhyme were on the seven banners of the
ships bearing each one of the seven
palantírs and so only duplicate the
palantírs, are not a separate seven. But
Elendil had gathered
nine ships not
seven, and when he and
Isildur were separted in the storm, he had four and Isildur (with Anárion) three, so there are no seven ships altogether. It is unfair to count the seven ships each carrying a
palantír as a separate seven from the
palantirs themselves.
The seven stars of
Gondor on
Aragorn’s standard are again the seven stars on the flags of Elendi”s ships.
The number of the
Valar I have already covered as possibly showing purposeful Judeo-Christian influence.
Possible
Balrogs: “There should not be supposed more than say 3 or at most 7 ever existed”. Not at all a definite seven.
Yet even subtracting the duplications and dropping the errors there are indeed still a lot of sevens in Tolkien.
But check
Number Seven and
7 Seven 7 for many sevens in the real world, some specifically connected with Christian symbolism, but most not.
Especially pertinent is:
Ask a number of different people to give you any number between one and ten, and most will choose seven. Ask people to name their favourite number between one and ten, and again most will say seven.
This explains a lot.
Seven just
is psychologically “magical”, and is so in all cultures and traditions so far as I know.
Tolkien, writing what is intended to be heroic romance and mythology, naturally and possibly not always consciously reflects this.
And of course, any set can be counted, and sometimes the number by chance will be seven.