Talk:Cleopatra/@comment-39255282-20190620191250/@comment-36277500-20190702123114

Not only Ptolemies - every Egyptian dynasty was endogamic.

Egyptian heirdom were not based on "father to son", but "father to daughter". So if a prince wanted to be a crown prince, he had to marry a crown princess... who was his sister...

Since Egyptians practiced polygamy (pharaoh had a harem), there were many half-siblings. So it was normal for a prince to marry his half-sister (I'm not sure about birth siblings).

Ptolemies didn't invent this, it was an archaic custom for thousands of years before them. People 2000 years BCE - they were as ancient to Cleopatra as she is ancient to us! - probably didn't know about genetics, but they knew about economy - they intended to save the wealth in the royal family, that's why they ordered endogamy in it.

However, Ptolemies didn't dare to break free from it. Even Cleopatra VII was forced to marry respectively her two brothers (and they both died in the civil war). Romancing Caesar and Antony was the best thing she could do, from the point of view of genetics.