House of Succession
[Assyrian] princes normally spent their early years in the harem, but while still fairly young were removed to be educated and trained for their future role in life. In the Sargonid period (and possibly earlier), the crown prince, once he had been officially so designated, entered the 'House of Succession'..., where he was surrounded by his own court and personal bodyguard. In this milieu he was prepared for his eventual elevation to the supreme position in the Assyrian state. Ashurbanipal tells us that it was in the House of Succession that he was trained both in military arts and intellectual pursuits, learning not only to ride and shoot but also to read and write. When the prince 'graduated' he was assigned to responsible duties in the empire, and in the Sargonid period, at least, the crown prince became the king's representative at home with regal authority while the father was campaigning. As to the rule of succession, we lack sufficient information both about the principle and about the practice, but it would appear that primogeniture was the guiding rule and in the odd case where it is known that the actual successor was not the eldest son, one may assume that his elder brother or brothers had died young, or been killed in a revolution led by the successful usurper.
— The Cambridge Ancient History, volume III, part 2, p. 198