A person of the name of Chæremon accompanied the governor, Ælius Gallus, in his journey from Alexandreia into Egypt, and pretended to some knowledge of this kind, but he was generally ridiculed for his boasting and ignorance. The houses of the priests, and the residences of Plato and of Eudoxus, were shown to us. Eudoxus came here with Plato, and, according to some writers, lived thirteen years in the society of the priests. For the latter were distinguished for their knowledge of the heavenly bodies, but were mysterious and uncommunicative, yet after a time were prevailed upon by courtesy to acquaint them with some of the principles of their science, but the barbarians concealed the greater part of them. They had, however, communicated the knowledge of the additional portions of the day and night, in the space of 365 days, necessary to complete the annual period; and, at that time, the length of the year was unknown to the Greeks, as were many other things, until later astronomers received them from the persons who translated the records of the priests into the Greek language, and even now derive knowledge from their writings and from those of the Chaldeans.[851] 30. After Heliopolis is the “Nile above the Delta.” The country on the right hand, as you go up the Nile, is called Libya, as well as that near Alexandreia and the lake Mareotis; the country on the left hand is called Arabia. The territory belonging to Heliopolis is in Arabia, but the city Cercesura is in Libya, and situated opposite to the observatory of Eudoxus. For there is shown an observing station in front of Heliopolis, as there is in front of Cnidus, where Eudoxus marked certain motions of the heavenly bodies. This is the Letopolite Nome. In sailing up the river we meet with Babylon, a strong fortress, built by some Babylonians who had taken refuge there, and had obtained permission from the kings to establish a settlement in that place. At present it is an encampment for one of the three legions which garrison Egypt. There is a mountainous ridge, which extends from the encampment as far as the Nile. At this ridge are wheels and screws, by which water is raised from the river, and one hundred and fifty prisoners are [thus] employed. The pyramids on the other side [of the river] at Memphis may be clearly discerned from this place, for they are not far off.