"The ancient customs are very many."

Translation: Mores antiqui sunt plurimi.

[Gridkeeper]

Why not "there are very many ancient customs"?
In English it doesn't flow to translate it to "the ancient customs are very many", it just looks like an unnecessary trick question.

[Tim568413]

Does word order matter here?

[SuzanneNussbaum]

I wrote Plurimi sunt mores antiqui and it wasn't accepted, though I think it should be. (Moving the predicate adj. to the beginning of the sentence in fact stresses it.)

[LouiviVeterus]

Though the verb usually goes at the end, word order is not strict and your answer should be correct.

[SuzanneNussbaum]

I believe that it's particularly the action verb, not the copula ("to be") that goes at the end of its clause.

A month later: still not accepted.

[PERCE_NEIGE]

If it wasn't accepted, it's only that they didn't add it to the database yet. Just report it, and it would be added.

[silvanarochford]

I agree. I wrote exactly the same and it was rejected

[dimork]

Plurimi sunt mores antiqui - why is this incorrect?

[SuzanneNussbaum]

This should be fine; this is a word order that puts emphasis on plūrimī , which seems appropriate. (See Berto's comment, just above yours.)

[SlavaBob]

also plurimi mores antiqui sunt was not accepted. If Latin is like Russian (also word order does not matter and lots of cases), when you put a word at the beginning it adds stress to it, so it sounds like you are saying "oh so very many customs" as if you're just in awe about how many customs there are, whereas the other way it sounds like you are just making a factual statement about customs.

[SuzanneNussbaum]

I think Latin does work that way: any time a word is moved out of its 'normal' or expected position, that adds emphasis, just as you say.

[SlavaBob]

And this sentence also doesn't make sense to me. If you are just making a factual statement, why say plurimi rather than multi? It seems to me the whole point of saying plurimi is to emphasize it, so putting plurimi at the beginning seems to make more sense.

[PERCE_NEIGE]

I don't think so. We cannot consider that all superlatives have to be at the beginning of the sentence. A search through texts show it is not the case.
Even if the superlative is a particular kind of emphasis (in one extend, it's not a real one), it's not the same emphasis than moving a word, as Suzanne explained it very well.

[chrisalbert123]

The English of this sentence is very poor indeed.

[KarenSwift3]

It looks like it is still marking the answer wrong if the word order differs (even though word order isn't supposed to matter)