There was a strong fortress situated at the head of the pier or mole leading to the island of Pharos, which was without Caesar's lines, and still in the hands of the Egyptian authorities. The Egyptians thus commanded the entrance to the mole. The island itself, also, with the fortress at the other end of the pier, was still in the possession of the Egyptian authorities, who seemed disposed to hold it for Achillas. The mole was very long, as the island was nearly a mile from the shore. There was quite a little town upon the island itself, besides the fortress or castle built there to defend the place. The garrison of this castle was strong, and the inhabitants of the town, too, constituted a somewhat formidable population, as they consisted of fishermen, sailors, wreckers, and such other desperate characters, as usually congregate about such a spot. Cleopatra and Caesar, from the windows of their palace within the city, looked out upon this island, with the tall light house rising in the center of it and the castle at its base, and upon the long and narrow isthmus connecting it with the main land, and concluded that it was very essential that they should get possession of the post, commanding, as it did, the entrance to the harbor.
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 Arsinoe's arrival in the camp there had been a constant rivalry and jealousy between himself and Ganymede, the eunuch who had accompanied Arsinoe in her flight. Two parties had been formed in the army, some declaring for Achillas and some for Ganymede. Arsinoe 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 Arsinoe's government as her minister of state and the commander-in-chief of her armies.
About the time that these occurrences took place, the Egyptian army advanced into those parts of the city from which Caesar had withdrawn, producing those terrible scenes of panic and confusion which always attend a sudden and violent change of military possession within the precincts of a city. Ganymede brought up his troops on every side to the walls of Caesar's citadels and intrenchments, and hemmed him closely in. He cut off all avenues of approach to Caesar's lines by land, and commenced vigorous preparations for an assault. He constructed engines for battering down the walls. He opened shops and established forges in every part of the city for the manufacture of darts, spears, pikes, and all kinds of military machinery. He built towers supported upon huge wheels, with the design of filling them with armed men when finally ready to make his assault upon Caesar's lines, and moving them up to the walls of the citadels and palaces, so as to give to his soldiers the advantage of a lofty elevation in making their attacks. He levied contributions on the rich citizens for the necessary funds, and provided himself with men by pressing all the artisans, laborers, and men capable of bearing arms into his service. He sent messengers back into the interior of the country, in every direction, summoning the people to arms, and calling for contributions of money and military stores.
These messengers were instructed to urge upon the people that, unless Caesar and his army were at once expelled from Alexandria, there was imminent danger that the national independence of Egypt would be forever destroyed. The Romans, they were to say, had extended their conquests over almost all the rest of the world. They had sent one army into Egypt before, under the command of Mark Antony, under the pretense of restoring Ptolemy Auletes to the throne. Now another commander, with another force, had come, offering some other pretexts for interfering in their affairs. These Roman encroachments, the messengers were to say, would end in the complete subjugation of Egypt to a foreign power, unless the people of the country aroused themselves to meet the danger manfully, and to expel the intruders.
As Caesar had possession of the island of Pharos and of the harbor, Ganymede could not cut him off from receiving such re-enforcements of men and arms as he might make arrangements for obtaining beyond the sea; nor could he curtail his supply of food, as the granaries and magazines within Caesar's quarter of the city contained almost inexhaustible stores of corn. There was one remaining point essential to the subsistence of an army besieged, and that was an abundant supply of water. The palaces and citadels which Caesar occupied were supplied with water by means of numerous subterranean aqueducts, which conveyed the water from the Nile to vast cisterns built under ground, whence it was raised by buckets and hydraulic engines for use. In reflecting upon this circumstance, Ganymede conceived the design of secretly digging a canal, so as to turn the waters of the sea by means of it into these aqueducts. This plan he carried into effect. The consequence was, that the water in the cisterns was gradually changed. It became first brackish, then more and more salt and bitter, until, at length, it was wholly impossible to use it. For some time the army within could not understand these changes; and when, at length, they discovered the cause the soldiers were panic-stricken at the thought, that they were now apparently wholly at the mercy of their enemies, since, without supplies of water, they must all immediately perish. They considered it hopeless to attempt any longer to hold out, and urged Caesar to evacuate the city, embark on board his galleys, and proceed to sea.