The assertion of the philosopher Simplicius has been called in question for very plausible reasons. Simplicius declares, upon the faith of Porphyrius, that Callisthenes sent from Babylon to his uncle Aristotle, a copy of Chaldaean observations dating back as far as 1903 years before the entry of Alexander into Mesopotamia, that is, to more than twenty-two centuries before our era.[100] However this may be, all ancient writers are agreed in admitting that the Chaldaeans had begun to observe and record astronomical phenomena long before the Egyptians;[101] moreover the remains of those clay tablets have been found in various parts of Chaldaea and Assyria upon which, as Pliny tells us upon the authority of the Greek astronomer Epigenes, the Chaldaeans had inscribed and preserved the astronomical observations of seven hundred and eighty thousand years.[102] We need not dwell upon the enormity of this figure; it matters little whether it is due to the mistakes of a copyist or to the vanity of the Chaldaeans, and the too ready credulity of the Greeks; the important point is the existence of the astronomical tablets, and those Epigenes himself saw. The library of Assurbanipal at Nineveh included catalogues of stellary and planetary observations, among others the times of Venus, Jupiter and Mars, and the phases of the moon, for every day in the month.[103] Tablets have also been recently discovered giving the arrangement of the stars in the sky for each season and explaining the rule to be followed in the insertion of the intercalary months. Finally, a fragment of an Assyrian planisphere has been found in the palace of Sennacherib.[104]