Yes it was but it was not known by most until Christopher Columbus did it, he is the one who really proved it to the world. On August 3 1492 He sailed from Palos Spain looking for the West Indies, and arrived on Oct 12, 1492 in the Bahamas. That means it took him 70 days to make the journey. At least he didn't sail off the Earth!
Back then it was believed that the Earth was flat, most everyone knew you couldn't sail around the world, you would fall off.
Christopher Columbus believed the world was round. He didnt know about Magellan, Christopher had a reason to believe the world was round. He had read in the Bible where God said, He sat on the sphere, (circle) of the earth. Columbus knew the Earth was round because God has said it was a sphere, a sphere is round like a circle. I thought you might like to know that. You can read about it yourself in the book of Isaiah chapter 40 verse 21. Christopher made this note in his journal.