After the Scythian-Parni nomads had settled in Parthia and built a small independent kingdom, they rose to power under king Mithridates the Great (171-138 BC). The power of the early Parthian empire seems to have been overestimated by some ancient historians, who could not clearly separate the powerful later empire from its more humble obscure origins. The end of this long-lived empire came in 224 AD, when the empire was loosely organized and the last king was defeated by one of the empire's vassals, the Persians of the Sassanid dynasty.