Lactantius
In the preface to De revolutionibus, Nicolaus Copernicus mocked Lactantius, an early Christian author (ca. 240 – ca. 320):
Perhaps there will be babblers who claim to be judges of astronomy although completely ignorant of the subject and, badly distorting some passage of Scripture to their purpose, will dare to find fault with my undertaking and censure it. I disregard them even to the extent of despising their criticism as unfounded. For it is not unknown that Lactantius, otherwise an illustrious writer but hardly an astronomer, speaks quite childishly about the earth's shape, when he mocks those who declared that the earth has the form of a globe. Hence scholars need not be surprised if any such persons will likewise ridicule me. Astronomy is written for astronomers.
A German TV documentary on "The seven greatest lies in history" states that medieval scholars knew full well that the Earth was a sphere. Copernicus is blamed for having omitted to say that Lactantius had been the exception rather than the rule, and thus for having contributed to the flat-Earth myth.
Read more about this topic: De Revolutionibus Orbium Coelestium