Vertimas - Lotynų-Anglų - Magnus erat numerus scriptorum antiquorum

'Magnus' means big, right?
As in a big amount of ancient writers?

The more I think of it, I guess it can also mean 'important' here. Any context?

Yes, "magnus" means "big" most of the time. But I often have some scrupules in front of the supposed nobililty of the latin language. I would not feel easy translating it by "the amount of ancient writers was just big"... See what I mean?
To make it short, "big" sounds a bit familiar.
Contexts?
For instance, "magnus princeps" becomes "Grand Prince" in French and English, "Great Prince" in English, and you have a large number of translations here http://en.wikipedia.org/wiki/Grand_Prince
"Big Prince" wouldn't sound right, would it?
Hope that answers your question