The Many Coloured House: Bet you didn't know... About Those Crazy Elamites!

Elam (Haltamti, in their own language) was a kingdom of ancient Iran, active before the Medes and Persians arose. Their kingdom lasted about 2000 years, from 2400-539BC. During that time they butted heads with the Sumerians, Babylonians, and Indus Valley people, among others.

Elam was a kingdom in two parts. The highland portion to the southeast, Elam proper, was ruled from the city of Anshan. The lowland portion (called Susiana) to the northwest was ruled from the already ancient city of Shushan, also known as Susa.

During their middle phase, Elamites had an unusual succession system by which there were three rulers:
The Sukkalmah (High Regent), was the highest office of the three - effectively the king.
The Sukkal of Elam (Regent of Elam) who was based in Anshan, and the Sukkal of Susa (Regent of Susa) were his co-rulers.

The Sukkal of Elam was away the brother of the Sukkalmah.

The Sukkal of Susa was the eldest son or nephew of the Sukkalmah.

When the Sukkalmah died, the brother in the position of Sukkal of Elam would become the new Sukkalmah, and the next brother in line (who may not yet have held a position) would become the new Sukkal of Elam. The Sukkal of Susa did not change. Only when all the Sukkalmah's brothers died would the son (or nephew) in the position of Sukkal of Susa become the new Sukkalmah, and his brother would become the new Sukkal of Elam, his son (or nephew) the new Sukkal of Susa.

So, in effect, whole families became joint rulers of this land. Family ties were obviously very important.

In later years this system would morph into something different, but the importance of family ties remained, and family drama would grow to George R.R. Martin-esque proportions.

From the Encyclopedia Iranica:

The inscriptions of [king] Šutruk-Nahhunte and his successors have revealed the practice of incest within the royal Elamite family.

The principal member of this family was Queen Nahhunte-utu. This altogether exceptional woman in Elamite history, and even in the ancient history of the Near East, bore ten children from four different fathers, who followed one another on the throne of Elam. From her father, she had at least two children, a son Hutelutuš-Inšušnak and a daughter, Inšnikarab-huhun. When he died, she married his elder brother, Kutir-Nahhunte, from whom she had two or three children. Shortly afterwards, the king was killed, and she then married his second brother Šilhak-Inšušinak, from whom she had 4 or 5 children. Finally, she gave birth to Melir-Nahhunte, a princess she had had from her own son, Hutelutš-Insušnak, whom she had had from her own father.