The article focuses on a very particular episode of the eastern Alexander legend, i.e. the building of an extraordinary “metal army” employed by Alexander in his war against the Indian King Porus, which is present in at least three Persian accounts written between the tenth and fourteenth centuries CE: the “Book of Kings” (Shāh-nāmeh) by Ferdowsi, the “Book of Dārāb” (Dārāb-nāmeh), attributed to Tarsusi, and an “Alexander-book” (Eskandar-nāmeh) in prose copied by ʿAbd al-Kāfi ibn Abu al-Barakāt. Compared to the most remote source, the text of Pseudo-Callisthenes, and to the closest ones (the Armenian version of the fifth century, the Syriac text of the sixth‒seventh centuries, and the Hebrew version of the tenth‒eleventh centuries), it is argued that the Persian authors have not passively received the inherited materials; on the contrary, they have been able to liven up the scene of Alexander’s battle against the Indian King Porus by bringing onto the battlefield a fiery and phantasmagorical army of metal, giving us one of the more amazing episodes in the eastern legend of the great Macedonian.