How Muslims believed earth was spherical long before anybody mentions it.

[Smaug]

Excuse me for repeating what may have been mentioned before in this topic but as far as I know some of the Greek philosophers arrived at a conclusion that the Earth was spherical well before the times of Christ. I don't remember who exactly introduced the idea but it was based roughly on the following reasoning: a drop of water tends to assume spheroidal figure when relatively isolated (falling down or resting on an even surface). Thus the drop's figure in the void woud've been perfectly spherical. Then this idea was extended to all the matter that formed the Earth. Also it was concluded that there were a central force that held everything in place on the Earth's surface. There also were other hypotheses introduced by the Greeks.

Also the Earth's radius had been measured by Eratosthenes well B. C. And by the the first century the roundness of the Earth was a relatively known fact in the civilized world (of that times). Well before the appearance of Islam. No wonder that Arabs may have known this fact since they paid much attention towards astronomy and philosophy in those times.