Translation:Centuries ago, people believed that the Earth was flat.
There's nothing wrong grammatically with the sentence, however, the fact behind it is incorrect.
Edit: 2015.07.18 - Why do I keep getting people replying to this comment saying that people believed in a Flat Earth only a couple of centuries ago? I've provided a source (and there are many others) that completely disprove this idea.
We have known about the spherical nature of the Earth since, at least, the Ancient Greeks (~500BC).