In the harbor, which was on the south side of the mole, and, consequently, on the side opposite to that from which Achillas was advancing toward the city, there were lying a large number of Egyptian vessels, some dismantled, and others manned and armed more or less effectively. These vessels had not yet come into Achillas's hands, but it would be certain that he would take possession of them as soon as he should gain admittance to those parts of the city which Caesar had abandoned. This it was extremely important to prevent; for, if Achillas held this fleet, especially if he continued to command the island of Pharos, he would be perfect master of all the approaches to the city on the side of the sea. He could then not only receive re-enforcements and supplies himself from that quarter, but he could also effectually cut off the Roman army from all possibility of receiving any. It became, therefore, as Caesar thought, imperiously necessary that he should protect himself from this danger. This he did by sending out an expedition to burn all the shipping in the harbor, and, at the same time, to take possession of a certain fort upon the island of Pharos which commanded the entrance to the port. This undertaking was abundantly successful. The troops burned the shipping, took the fort, expelled the Egyptian soldiers from it, and put a Roman garrison into it instead, and then returned in safety within Caesar's lines. Cleopatra witnessed these exploits from her palace windows with feelings of the highest admiration for the energy and valor which her Roman protectors displayed. The burning of the Egyptian ships in this action, however fortunate for Cleopatra and Caesar, was attended with a catastrophe which has ever since been lamented by the whole civilized world. Some of the burning ships were driven by the wind to the shore, where they set fire to the buildings which were contiguous to the water. The flames spread and produced an extensive conflagration, in the course of which the largest part of the great library was destroyed. This library was the only general collection of the ancient writings that ever had been made, and the loss of it was never repaired. The destruction of the Egyptian fleet resulted also in the downfall and ruin of Achillas. From the time of Arsinoë's arrival in the camp there had been a constant rivalry and jealousy between himself and Ganymede, the eunuch who had accompanied Arsinoë in her flight. Two parties had been formed in the army, some declaring for Achillas and some for Ganymede. Arsinoë advocated Ganymede's interests, and when, at length, the fleet was burned, she charged Achillas with having been, by his neglect or incapacity, the cause of the loss. Achillas was tried, condemned, and beheaded. From that time Ganymede assumed the administration of Arsinoë's government as her minister of state and the commander-in-chief of her armies.