> I don't know of any that did bother and decided it was flat (and would really like a pointer) 天圓地方 (literally: sky round, land square) was a serious core ide

> I don't know of any that did bother and decided it was flat (and would really like a pointer) 天圓地方 (literally: sky round, land square) was a serious core idea in ancient Chinese cosmology that was most popular 2000 years ago around the Han Dynasty period. As for some serious pointers as you requested, here: https://ctext.org/lunheng/shuo-ri/zh https://ctext.org/lunheng/shuo-ri/zh There's a couple paragraphs arguing that the sky isn't round (dome-like) but "flat" and parallel to the land because people have travelled and have never seen the sky merge with the land. (see the paras starting "實者、天不在地中，日亦不隨天隱，天平正，與地無異。") You might say the ancient Chinese didn't care enough so they ended up with wrong conclusions (or parroted whatever was told to them by even more ancient sources that just made up its cosmology), but at any rate the Chinese definitely did believe in flat earth 2000 years ago, and we have very reliable records for that one.