Roman History, 42.38
38Meanwhile Achillas arrived with the Romans and the others who had been left behind with Septimius by Gabinius to keep guard over Ptolemy; for these troops as a result of their stay there had changed their habits and had adopted those of the natives. And he immediately won over the larger part of the Alexandrines and made himself master of the most advantageous positions. 2After this many battles occurred between the two forces both by day and by night, and many places were set on fire, with the result that the docks and the storehouses of grain among other buildings were burned, and also the library, whose volumes, it is said, were of the greatest number and excellence. Achillas was in possession of the mainland, with the exception of what Caesar had walled off, and the latter of the sea except the harbour. 3Caesar, indeed, was victorious in a sea-fight, and when the Egyptians, consequently, fearing that he would sail into their harbour, had blocked up the entrance with the exception of a narrow passage, he cut off that outlet also by sinking freight ships loaded with stones; so they were unable to stir, no matter how much they might desire to sail out. 4After this achievement provisions, and water in particular, were brought in more easily; for Achillas had deprived them of the local water-supply by cutting the pipes.