I think Colombus ansered that question some centuries ago, you can travel too all AROUND the earth and see for yourself...also there are instruments that show as the Earth is a shpere , sooo even if we forget about the millions of satelites orbiting the Earth ( in order to...orbit you need a sphere) there are ancient instruments to prove it.
Speakin' of ancient instruments ...

I think she was a middle-distance runner...
(The translation wasn't clear).
Could be a budding stately hero.
International competition in a year.
She was a good enough reason for a party...
(Well, you couldn't keep up on a hard track mile)
While she ran a perfect circle.
And she wore a perfect smile
In Budapest... hot night in Budapest.
We had to cozzy up in the old gymnasium...
Dusting off the mandolins and checking on the gear.
She was helping out at the back-stage...
Stopping hearts and chilling beer.
Yes, and her legs went on for ever.
Like staring up at infinity
Through a wisp of cotton panty
Along a skin of satin sea.
Hot night in Budapest.