The Reign of Wizardry by Jack Williamson. Here is the first book appearance of a novel which originally appeared in Unknown as a 3 part serial beginning in March 1940. From the back cover: "The Walls of Sorcery: Before the glory of Greece, Crete ruled the known world - and kept it enslaved by black magic. The evil of Minos held sway, protected by the three unconquerable walls... First there is the fleet, that they call the wooden wall. Then there is a giant of living brass - he is the second wall. Then there is another barrier about the power of Minos: The Wall of Wizardry! Theseus, the tall Achean - the man they called Captain Firebrand - vowed to scale and destroy all three, and to rid the world of the evil yoke of Minos. But Minos had other defences besides the three walls - and many ways to attack, as well..."