In return for the literature which Greece then gave to Egypt, she gained the knowledge of papyrus, a tall rush which grows wild near the sources of the Nile, and was then cultivated in the Egyptian marshes. Before that time books had been written on linen, wax, bark, or the leaves of trees; and public records on stone, brass, or lead: but the knowledge of papyrus was felt by all men of letters like the invention of printing in modern Europe. Books were then known by many for the first time, and very little else was afterwards used in Greece or Rome; for, when parchment was made about two centuries later, it was too costly to be used as long as papyrus was within reach. Copies were multiplied on frail strips of this plant, and it was found that mere thoughts, when worth preserving, were less liable to be destroyed by time than temples and palaces of the hardest stone. [Illustration: 056.jpb MANUSCRIPT ON PAPYRUS; HIEROGLYPHICS, THEBES] While Egypt, under Ptolemy, was thus enjoying the advantages of its insulated position, and cultivating the arts of peace, the other provinces were being harassed by the unceasing wars of Alexander's generals, who were aiming, like Ptolemy, at raising their own power. Many changes had taken place among them in the short space of eight years which had passed since the death of Alexander. Philip Arridaeus, in whose name the provinces had been governed, had been put to death; Antigonus was master of Asia Minor, with a kingdom more powerful though not so easily guarded as Egypt; Cassander held Macedonia, and had the care of the young Alexander AEgus, who was then called the heir to the whole of his father's wide conquests, and whose life, like that of Arridaeus, was soon to end with his minority; Lysimachus was trying to form a kingdom in Thrace; and Seleucus had for a brief period held Babylonia. Ptolemy bore no part in the wars which brought about these changes, beyond being once or twice called upon to send troops to guard his province of Cole-Syria. [Illustration: 057.jpg Alexander adoring Horus] But Antigonus, in his ambitious efforts to stretch his power over all the provinces, had by force or by treachery driven Seleucus out of Babylon, and forced him to seek Egypt for safety, where Ptolemy received him with the kindness and good policy which had before gained so many friends. No arguments of Seleucus were wanting to persuade Ptolemy that Antigonus was dreaming of universal conquest, and that his next attack would be upon Egypt. He therefore sent ambassadors to make treaties of alliance with Cassander and Lysimachus, who readily joined him against the common enemy.