A distinct Thessalian tribal identity and culture first began to form from the 9th century BC on as a mixture of the local population and immigrants from Epirus, first in the region of the Pelasgiotis, with Pherae as its main centre. From there they quickly expanded inland to the plain of the Pineios and towards the Malian Gulf. The Thessalians spoke a distinct form of Aeolic Greek. In the late 7th century BC, the Thessalians conquered the so-called "perioikoi". In this process the Thessalians captured Anthela and came to control the local amphictyony. By assuming the former share of the "perioikoi" in the Delphic Amphictyony, the Thessalians also came to play a leading role in the latter, providing 14 of the 24 "hieromnemones" and presiding over the Pythian Games. As a result of the First Sacred War (595–585 BC), the Thessalians briefly extended their sway over Phocis as well, but the Boeotians drove them back after the battles of Hyampolis and Ceressus in the mid-6th century.