of power within Scythia shifted to the south, in the region of the bend of the Dnipro, where the site of Kamianka became the principal industrial centre of Scythia, with the sedentary population of the city being largely metal-workers who smelted bog iron ores into iron that was made into tools, simple ornaments and weapons for the agricultural population of the Dnipro valley and of other regions of Scythia, and the city itself was the most prominent supplier of iron and bronze products to the nomadic Scythians; the city of Kamianka also became the capital of the Scythian kings, whose headquarters were located in the further fortified acropolis of the city. At the same time, a wave of Sauromatian nomads from the lower Volga steppe in the east immigrated into Scythia over the course of 550 and 500 BC and were absorbed by the Pontic Scythians with whom they mingled. A large number of settlements in the valleys of the steppe rivers being destroyed as a result of these various migratory movements. The retreat of the Scythians from the Kuban Steppe and the arrival of the Sauromatian immigrants into the Pontic steppe over the course of the late 6th to early 5th centuries BC caused significant material changes in the Scythian culture soon after the Persian campaign which are not attributable to a normal evolution of it, resulting in the sudden appearance within the lower Dnipro region of a fully formed Scythian culture with no local forerunners, and which included a notable increase in the number of Scythian funerary monuments. The Scythians underwent tribal unification and political consolidation in reaction to the Persian invasion, and they also became more active and aggressive around this time, possibly as a result of the arrival of these new nomadic elements, or out of necessity to resist Persian expansionism. This change manifested itself through the consolidation of the dominant position of the Royal Scythians over the other tribes within Scythia and through the Royal Scythians' hold on the western part of their realm to the west of the Dnipro, where lived the agriculturist populations, becoming heavier and more oppressive. Another result of the changes within Scythia during this period was increased Scythian expansionism: one of the target areas of Scythian expansionism was Thrace, where the Scythians seem to have established a permanent presence to the south of the Danube at an early point, with