The external casing of the pyramid has entirely disappeared, as we have already said. On account of their moderate size the stones of which it was composed would seem to be especially well fitted for use in building those great cities which, after the collapse of the ancient civilization, succeeded each other, under different names, in the neighbourhood of the Memphite necropolis. This casing seems to have been made of more than one kind of stone, if we may believe an ancient text which has been interpreted by Letronne with the skill and sagacity of which he has given so many proofs.[208] [208] These observations are to be found in one of the early works of Letronne. Their presence is in no way hinted at by the title, which is: _Recherches Géographiques et Critiques sur le Livre 'De mensura orbis terræ'_ (8vo. 1844). The treatise, Περὶ τῶν ἑπτὰ θεαμάτων, may have been written either by Philo of Heraclea or Philo of Byzantium. They both belonged to the third century before our era, but the bombastic style and numerous errors incline us to believe that the little work must have been from the pen of some unknown rhetorician of a later date. The author, named Philo, of a treatise upon the Seven Wonders of the World, tells us that the Egyptians employed upon this work "the most brilliant and varied stones, which were carefully fixed." He mentions as contributing to the splendid result white marble, basalt, porphyry, and a green breccia from Arabia, which must have been what is called _verde antique_. And as for his white marble, it must have been the white limestone from Mokattam, which, in its best strata, is almost as white and fine in grain as marble. Marble, properly speaking, was only introduced into Egypt by the Greeks, and that in very small quantities, for the use of sculptors. Philo says nothing of granite, but its use was so general that it must have found a place in the scheme of decoration.[209] [209] These are the words of Philo, which we have translated rather freely:-- Ποικίλαι δὲ καὶ πορφυραὶ λίθων φύσεις ἀλλήλαις ἐπιδεδόμεναι, καὶ τὰ μέν ἐστιν ἡ πέτρα λευκὴ καὶ μαρμαρίτης· τῇ δὲ Αἰθιοπικὴ καὶ μέλαινα καὶ μετὰ ταύτην ὁ καλούμενος αἱματίτης λιθος· εἶτα ποικίλος καὶ διάχλωρος ἀπὸ τῆς Ἀραβίας κεκομισμένος, p. 2,259, A. The various kinds of stone must have been so placed as to form zones, and perhaps patterns, of different colours, white, red, black, rose, green, and so on. To form an idea of the effect we must think of Giotto's campanile at Florence and various other Italian buildings of the same kind.