Egyptian cities seem always to have been surrounded by a fortified _enceinte_; in some cases the remains of such fortifications have been found, in others history tells us that they existed. At Thebes, for instance, no traces have, so far as we know, been discovered of any wall. Homer's epithet of _hundred-gated_ (ἑκατόμπυλος) may be put on one side as evidence, because the Greek poet did not know Egypt. He described the great metropolis of the Empire of the South as he imagined it to be. The Homeric epithet is capable also of another explanation, an explanation which did not escape Diodorus,[34] it may have referred, not to the gates of the city, but to the pylons of the temples, and should in that case be translated as "_Thebes of the hundred pylons_" instead of hundred gates. We have better evidence as to the existence of fortifications about the town in the descriptions left to us by the ancient historians of the siege of Ptolemy Physcon: the city could not have resisted for several years if it had been an open town. It was the same with Memphis. On more than one occasion, during the Pharaonic period as well as after the Persian conquest, it played the part of a fortress of the first class. It was the key of middle Egypt. It even had a kind of citadel which included almost a third of the city and was called the _white wall_ (λευκὸν τεῖχος).[35] This name was given, as the scholiast to Thucydides informs us, "because its walls were of white stone, while those of the city itself were of red brick." The exactness of this statement may be doubted. The Egyptians made their defensive walls of a thickness which could only be attained in brick. It seems likely therefore that these walls consisted of a brick core covered with white stone. An examination of the remains of Heliopolis suggested to the authors of the _Description de l'Égypte_ that the walls of that city also were cased with dressed stone. They found, even upon the highest part of the walls, pieces of limestone for which they could account in no other way. [34] DIODORUS, i. 45, 6. [35] THUCYDIDES, i. 104. Cf. HERODOTUS, iii. 94, and DIODORUS, xi. 74. After the Persian conquest it was occupied by the army corps left to ensure the submission of the country.