The pharaonic custom of having princesses marry their brothers and rule as sister-queens had a well-thought political rationale behind. These marriages were rarely consummated and any offspring produced normally were unfit for power, so most pharaohs were sons by their predecessor's non-related wives or concubines. However, brotherly marriages meant that Egypt’s royal princesses typically didn’t marry outside of the family. As it's very evident from the comparison between Egypt's relative...
