were ruled by a succession of kings whose names were recorded by Herodotus of Halicarnassus: Spargapeithes Lykos, son of Spargapeithes Gnouros, son of Lykos Saulios, son of Gnouros Idanthyrsus, son of Saulios At the time of Idanthyrsus, and possibly later, the Scythians were ruled by three kings, with Scopasis and Taxacis ruling alongside him. The Persian invasion In 513 BC, the king Darius I of the Persian Achaemenid Empire, which had succeeded the Median, Lydian, Egyptian, and Neo-Babylonian empires which the Scythians had once interacted with, carried out a campaign against the Pontic Scythians, for unclear reasons. Darius's invasion was resisted by the Scythian king Idanthyrsus, who led the combined forces of the Scythians and their neighbouring peoples, and by the kings Skōpasis and Taxakis, with the Scythians refused to fight an open battle against the well-organised Achaemenid army, and instead resorting to partisan warfare and goading the Persian army deep into Scythian territory. The Persian army might have crossed the Don river and reached the territory of the Sauromatians, were Darius built fortifications, but resumed their pursuit when the Scythian forces returned. The results of this campaign were also unclear, with the Persian inscriptions themselves referring to the (the "Saka who dwell beyond the (Black) Sea"), that is to the Scythians, as having been conquered by Darius, while Greek authors instead claimed that Darius's campaign failed and from then onwards developed a tradition of idealising the Scythians as being invincible thanks to their nomadic lifestyle. Early decline Over the course of the late 6th century BC, the Scythians had progressively lost their territories in the Kuban region to another nomadic Iranian people, the Sauromatians, beginning with the territory to the east of the Laba river, and then the whole Kuban territory. By the end of the 6th century BC, the Scythians had lost their territories in the Kuban Steppe and had been forced to retreat into the Pontic Steppe, except for its westernmost part which included the Taman peninsula, where the Scythian Sindi tribe formed a ruling class over the native Maeotians, due to which this country was named Sindica. By the 5th century BC, Sindica was the only place in the Caucasus where the Scythian culture survived. Expansion After losing their territories in the Kuban Steppe in the late 6th century BC, the Scythians had being forced to retreat into the Pontic Steppe, and the Royal Scythians' centre