When Argrath succeeded to the throne of Sartar in 1627, he took possession of a kingdom beset by enemies on all sides, and on the verge of collapse. The previous Prince, Kallyr Starbrow, had been killed in a disastrous battle against Tarshite invaders, led by King Pharandros. The Sartarites defeated the Tarshites, but at a high cost. Tribal leaders were disunited and at each others throats.
Argrath immediately saw that in order for Sartar to keep its freedom, it would need to become the dominant, significant military power in Dragon Pass. To do this reforms were required, and the equivalent of the Lunar College of Magic would need to be created. Magicians and cavalry, initially Praxian cavalry, would become the decisive arm of the Sartarite army.
Within the first two years of his reign, Argrath defeated the Lunar Army and secured Sartar’s borders. He achieved this remarkable feat through a number of ways, not all of them military; he was much admired and renowned for his political shrewdness.
Now this is just a loosely adapted summary of the start of Philip II of Macedon’s reign, but it applies well to Argrath and Sartar. Argrath is more of an Alexander figure in idealized heroism, but had to do Philip’s hard work rebuilding the kingdom. Philiip became king in 359 and Alexander died in 323, so together they ruled 36 years. Argrath ruled from 1627 to his apotheosis in 1658, so 31, which is pretty comparable.