Ammon (Greek Ἄμμων) was a geometrician who made a measurement of the walls of Rome, around the time of the first invasion of the Goths, that is, the 3rd century AD, and found them to be 21 miles in circumference.[1][2]
This article incorporates text from a publication now in the public domain: Smith, William, ed. (1870). "Ammon". Dictionary of Greek and Roman Biography and Mythology.