The Aorsi and an associated tribe, the Siraces, are believed to have migrated during the late 5th century BC from Central Asia to areas north and west of the Caspian Sea. The territory of the Aorsi is believed to have extended eastwards as far as the Aral Sea. The most important contemporaneous source on the Aorsi was the Greek geographer Strabo, in Geographica. Strabo suggested that the Aorsi were located north-east of the Siraces, who inhabited the area between Lake Maeotis and the Caspian. Furthest to the east lived the Upper Aorsi. They held the largest territory, dominating according to Strabo the Caspian coast, which enabled them to become the most numerous faction. The Upper Aorsi imported Indian and Babylonian merchandise by camel through Armenia and Media, which enabled them to become wealthy. They controlled the northern part of the Silk Route, known as the Northern Route. The Aorsi became famous for their wearing of golden ornaments. During the reign of Pharnaces II of the Bosporan Kingdom, according to Strabo, king Spadines of the Aorsi along the Tanais could muster a force of 200,000 horsemen, while the Upper Aorsi could muster even more. In the Annals, Tacitus writes that in the Bosporan War of 49 AD, the Adorsi king Eunones supported the Pro-Roman faction of Tiberius Julius Cotys I, while the kingZorsines of the Siraces supported the anti-Roman Tiberius Julius Mithridates. Together with Roman cohorts and Roman-armed Bosporans, the Aorsi besieged the poorly fortified town of the Siraces and massacred its population, forcing their king Zorsines to yield hostages and prostrate himself before the image ofEmperor Claudius. Facing inevitable defeat, Mithradates surrendered and threw himself before the feet of Eunones. Eunones was deeply moved by Mithradates' plight, and sent envoys to Claudius supporting Mithradates' request to be executed without a triumph. Claudius agreed in a letter to Eunones, and although Mithradates was eventually brought to Rome through Pontus, he was spared from execution and instead exiled. After the Bosporan War the Siraces were significantly weakened while the Aorsi rose in strength.
Many scholars have equated both the Aorsi and Alans to the state of Yancai, also known as Alanliao, which was mentioned in earlier Chinese records. The 2nd century BC diplomat Zhang Qian, reported that Yancai lay 2,000 li north-west of the state of Kangju, in the Ferghana Valley, with which it shared similar customs. Yancai was centered near the Aral Sea and able to muster 100,000 mounted archers. This location on the Eurasian Steppe was similar to that reported for the Aorsi by sources such as Strabo. A chronicle of the Later Han Dynasty, the Hou Hanshu – covering the period 25–220, but not completed until the 5th century, mentioned a report that Yancai had become a vassal state of Kangju, and was now known as Alanliao. Y. A. Zadneprovskiy suggests that the subjugation of Yancai by Kangju occurred in the 1st century BC. The westward expansion of Kangju obliged many of the Aorsi and other Sarmatians to migrate westwards. This migration contributed significantly to the Migration Period in Europe, which played an important role in world history. In the 1st century AD, the Alans achieved a dominant position among the Sarmatians living between the Don River and the Caspian Sea. The Alans were a people from the east closely related to the Aorsi, whom they either absorbed or conquered. Some of the Aorsi appear to have migrated west to the north of Crimea, where they maintained a semi-independent existence. Ptolemy speaks of the Alanorsi, suggesting that a fusion of some sorts between them had occurred.
