"The Power of Words in Ancient Greek and Roman Magic" as an ancient title would be
Περὶ τῆς δυνάμεως τῶν λόγων τῶν ἐν τῇ μαγευτικῇ τῶν ἀρχαίων Ἑλλήνων τε καὶ Ῥωμαίων χρησθέντων
— literally, "On the power of words used in the magic of the ancient Greeks and Romans."
Transliterated with Roman letters, it would be
Peri tês dynameôs tôn logôn tôn en têi mageutikêi tôn archaiôn Hellênôn te kai Rômaiôn chrêsthentôn