He then took Arsinoë, his own sister, as the partner of his throne. She had married first the old Lysimachus, King of Thrace, and then Ceraunus, her half-brother, when he was King of Macedonia. As they were not children of the same mother, this second marriage was neither illegal nor improper in Macedonia; but her third marriage with Philadelphus could only be justified by the laws of Egypt, their adopted country. They were both past the middle age, and whether Philadelphus looked upon her as his wife or not, at any rate they had no children. Her own children by Lysimachus had been put to death by Ceraunus, and she readily adopted those of her brother with all the kindness of a mother. She was a woman of an enlarged mind; her husband and her stepchildren alike valued her; and Eratosthenes showed his opinion of her learning and strong sense by giving the name of Arsinoë to one of his works, which perhaps a modern writer would have named Table-talk.
This seeming marriage, however, between brother and sister did not escape blame with the Greeks of Alexandria. The poet Sotades, whose verses were as licentious as his life, wrote some coarse lines against the queen, for which he was forced to fly from Egypt, and, being overtaken at sea, he was wrapped up in lead and thrown overboard.
In the Egyptian inscriptions Ptolemy and Arsinoë are always called the brother-gods; on the coins they are called Adelphi, the brothers; and afterwards the king took the name of Philadelphus, or sister-loving, by which he is now usually known. In the first half of his reign Philadelphus dated his coins from the year that his father came to the throne; and it was not till the nineteenth year of his reign, soon after the death of his mother, that he made an era of his own, and dated his coins by the year of his own reign. The wealth of the country is well shown by the great size of those most in use, which were, in gold the tetra-stater or piece of eight drachms, and in silver the tetra-drachma, or piece of four drachms, while Greece had hardly seen a piece of gold larger than the single stater. In Alexandrian accounts also the unit of money was the silver didrachm, and thus double that in use among the merchants of Greece.
Among the coins is one with the heads of Soter and Philadelphus on the one side, and the head of Berenicê, the wife of the one and mother of the other, on the other side. This we may suppose to have been struck during the first two years of his reign, in the lifetime of his father. Another bears on one side the heads of Ptolemy Soter and Berenicê, with the title of “the gods,” and on the other side the heads of Philadelphus and his wife Arsinoë, with the title of “the brothers.” This was struck after the death of his parents. A third was struck by the king in honour of his queen and sister. On the one side is the head of the queen, and on the other is the name of “Arsinoë, the brother-loving,” with the cornucopia, or horn of Amalthea, an emblem borrowed by the queens of Egypt from the goddess Amalthea, the wife of the Libyan Anion. This was struck after his second marriage.
On the death of Arsinoë, Philadelphus built a tomb for her in Alexandria, called the Arsinoëum, and set up in it an obelisk eighty cubits high, which had been made by King Nectanebo, but had been left plain, without carving.
Satyrus, the architect, had the charge of moving it. He dug a canal to it as it lay upon the ground, and moved two heavily laden barges under it. The burdens were then taken out of the barges, and as they floated higher they raised the obelisk off the ground. He then found it a task as great or greater to set it up in its place; and this Greek engineer must surely have looked back with wonder on the labour and knowledge of mechanics which must have been used in setting up the obelisks, colossal statues, and pyramids, which he saw scattered over the country. This obelisk now ornaments the cathedral of the Popes on the Vatican hill at Rome. Satyrus wrote a treatise on precious stones, and he also carved on them with great skill; but his works are known only in the following lines, which were written by Diodorus on his portrait of Arsinoë cut in crystal: