IIRC what Columbus didn't know was Eratosthones calculation of the circumference of the Earth that was <1% off, but believed Ptolemy's ~30% short estimation and

IIRC what Columbus didn't know was Eratosthones calculation of the circumference of the Earth that was <1% off, but believed Ptolemy's ~30% short estimation and figured there was no land in between Europe and the East Indies.