What prompted the Greek Ptolemaic Pharaohs to adopt brother-sister incest within a single generation?

cleopatra_philopater: A major misconception about the adoption of full-sibling marriage by the Ptolemaic dynasty is that it was mostly an attempt to legitimise their Pharaonic rule and uphold Egyptian tradition. This is incorrect for two reasons, the first being that the practice of Pharaohs marrying their royal sisters was neither mandatory or even all that common throughout Egyptian Dynastic history, it did occur and royal princesses were often wed to relatives rather than have them marry below their rank, but the idea of Egyptian dynasties simply marrying into themselves in an unbroken line is in no way accurate. Second, is that Ptolemy II had a strong political reason to marry Arsinöe II that had nothing to do with Egyptian traditions; to deny her to their half-brother Ptolemy Keraunos.

Arsinöe II had first been married to Lysimachus as part of the alliance between him and Ptolemy I (father of Ptolemy II, Keraunos and Arsinöe II), and she bore Lysimachus three sons. Through her marriage to Lysimachus she had a potential claim to his kingdom of Macedon and Thrace which was strengthened once she arranged for Aagathocles (Lysimachus’ son from a previous marriage) killed. So having established Arsinöe’s position, let us move on to Keraunos.

Ptolemy Keraunos was actually the oldest son of Ptolemy I *but* he was passed up in the succession and his younger half-brother Ptolemy II was named heir apparent instead so Keraunos fled Egypt and found sanctuary at the court of Lysimachus as he did not want to be in the position of a potential rival for the throne. Lysimachus was later killed in battle when he was defeated by the forces of Seleucus Nicator, and Keraunos later had Seleucus killed and asserted control over Thrace and Macedon. This however had the unfortunate effect of leaving Arsinöe II and her sons in a precarious position because of their potential claims so to neutralise this tense situation Keraunos married her. This sounds shocking by our standards but in many Hellenic societies like Athens and Macedon it was perfectly acceptable for paternal (but not maternal) half-siblings to marry, and even in Greek city-states and other states like Rome which did not permit this, occurrences like the marriage of women to first-cousins or uncles was nothing to bat an eye at. Even their rivals the Seleucids had half-sibling unions in their dynasty. This marriage would prove to be an unhappy one, and Arsinöe II plotted against Keraunos with her sons which he punished by murdering the two youngest while her firstborn escaped.

It was now Arsinöe’s turn to flee and she went to Egypt seeking the protection of her brother Ptolemy II who was at the time married to Arsinöe I a distant cousin of theirs who happened to have the same name. Arsinöe II then turned her apparently formidable talent for intrigues and political machinations to work by building alliances in the Alexandrian court and convincing Ptolemy II to divorce Arsinöe I and marry her instead. Although the Macedonians practiced polygyny and the divorce and dismissal of Arsinöe I was not necessary for the marriage to Arsinöe II to occur, it was necessary for Arsinöe II to establish herself as Ptolemy’s undisputed queen-regent. It was said that this marriage was genuinely loving and that Ptolemy at least was interested in the marriage for personal as well as political reasons. However this was also a smart move for Ptolemy II as by marrying Arsinöe II he prevented someone else from marrying her and claiming any territories as part of her dowry, and it seems that Arsinöe II was able to aid Ptolemy’s cause on the political front in Egypt as well since she was fairly popular in Alexandria.

The union of Ptolemy II and Arsinöe II was received with shock and distaste from their Greek subjects as full-sibling unions fell outside of what was acceptable to Hellenic sensibilities. According to the Roman Alexandrian historian Plutarch, a poet named Sosibius the Obscene mocked the union in a poem which accused Ptolemy II in a most, uncouth, manner with the line
>you are sticking your prick in an unholy hole

Needless to say, neither Ptolemy II or Arsinöe II found this as amusing as Sosibius did and one of Ptolemy’s admirals by the name of Patroklus had him sealed in a lead box and tossed into Lake Mareotis outside of Alexandria. Roman sources also express distaste for what they saw as an outgrowth of “Oriental” degeneracy and the incestuous heritage of the Ptolemies was frequently invoked to demonstrate their tyranny and moral decay.

But poetry was also used to *justify* the union as in the case of Theokritus, a patron of the Alexandrian court, composed poems praising the union and comparing it to the divine sibling-spouses Zeus and Hera. By making a connection to Greek mythology the union was taken out of the context of a sordid disgrace and instead cast in the light of that which is pure and godlike.
>From Zeus let us begin, and with Zeus in our poems, Muses, let us make end, for of immortals he is best; but of men let Ptolemy be named, first, last, and in the midst, for of men he is most excellent… he and his noble wife, than whom none better clasps in her arms a husband in his halls, loving with all her heart her brother and her spouse. After this fashion was accomplished the sacred bridal also of the immortals whom Queen Rhea bore to rule Olympus; and single is the couch that Iris, virgin still, her hands made pure with perfumes, strews for the sleep of Zeus and Hera.

The emphasis on purity and divinity through sibling-marriage would continue to be used throughout Ptolemaic dynastic history but it was more a call-back to the reign of Ptolemy II and Arsinöe II than to the Pharaonic traditions that had passed. The comparison to the Egyptian gods Isis and Osiris was also made of course, but even here they tended to view and present these deities in Hellenic terms as the Egyptian equivalents of Zeus and Hera. In general, whenever the Ptolemies used Egyptian ideology to justify their peculiarities to Greek subjects, it was closer to Greek perceptions of Egypt than to the realities of Egyptian culture. It is also worth noting that although we have evidence that in the Roman period upwards of 20% of marriages were between siblings, this is thought to have *increased* from in the Ptolemaic period and although the reasons for this is very unclear it seems that many of the practices that were so specifically “Egyptian” were specific to decidedly un-Egyptian periods.

Arsinöe II and Ptolemy II had no children, despite their apparently happy marriage and Arsinöe I’s son Ptolemy III would inherit the throne and marry the Cyrenean princess Berenike. The reasons why this practice was continued is that it was useful to limit the amount of claimants to the throne, and on many occasions civil wars or rivalries between vying siblings were resolved through marriage. Take the case of the infamous marriage between Ptolemy VIII, Cleopatra II and Cleopatra III. At first glance, the marriage of Ptolemy VIII to his sister and then to her daughter who was herself the daughter of Cleopatra II their deceased brother Ptolemy VI is horrifying. To be fair, it remains distasteful in context but it was not motivated by incestuousness or depravity. Ptolemy VIII first married Cleopatra II to secure his claim on the throne since he had unsuccessfully attempted to overthrow her and Ptolemy VI before the latter’s death in a war in Syria. By marrying her he ended the civil war between them but he would end up murdering her sons so he would have no rivals and also married her 14 year old daughter Cleopatra III before exiling Cleopatra II. This was almost certainly forced on Cleopatra III but the young queen still actively vied with her mother for the throne, and after Cleopatra II returned to power she exiled her daughter and husband both. This led to further conflicts which plunged Egypt into anarchy until a settlement was reached where the three reconciled and ruled jointly, with Cleopatra III’s children by Ptolemy VIII coming to power after his death. This knotted web of incest was directly caused by the internecine conflicts of the time, which were in turn fueled by the ambitions of the claimants and the various officials and courtiers who jockeyed for royal favour and greater influence.

The overall situation was not so much a conscious decision to adhere to any Egyptian politico-religious standard as it was a series of instances where monarchs and the advisors guiding them found it useful to employ an (eventually) unobjectionable means of neutralising rival successors.

It is relevant to point out that the first Ptolemaic ruler born of a full-sibling marriage was *Ptolemy V* and he married a Seleucid princess named Cleopatra I, so in all, the amount of inbreeding in the Ptolemaic dynasty is often overestimated since it is assumed that each full-sibling marriage produced children who then wed which was simply not the case.