We have now followed the fortunes of science as it came to Europe from the east, first impinging on Ionian Greece and then penetrating to Athens, to various outlying parts of the Greek mainland and to southern Italy. Finally, when its light was already beginning to fade in Greece, it turned eastward again and found a home in Alexandria, the magnificent city which Ptolemy I had built at the mouth of the Nile.

Here many subjects of study had seemed to work themselves out to their natural endings. Geometry, which had made such magnificent progress at first, came to a dead end; algebra had hardly yet arrived; physics, which had made a good start, had been strangled almost at birth; astronomy, after making the best of starts, had taken a wrong turning at the time of Aristarchus, and was now advancing along the wrong road.

Worst of all was the opposition of religion. We have seen how the Christians had burned a large part of the great library in 390; in 415 they had murdered Hypatia; and in 642 the Mohammedans conquered the city, closed down the university and completed the destruction of the library. Each attack drove a part of the school abroad, so that learning and learned men were scattered to many lands—to Greece, to Rome, to Byzantium, even to Persia and the east. We shall now see how these scattered threads were all drawn together in the great medieval empire founded by the Arabs.