The Macedonians were an ancient tribe that lived on the alluvial plain around the rivers Haliacmon and lower Axios in the northeastern part of mainland Greece. Essentially an ancient Greek people, they gradually expanded from their homeland along the Haliacmon valley on the northern edge of the Greek world, absorbing or driving out neighbouring non-Greek tribes, primarily Thracian and Illyrian. They spoke Ancient Macedonian, which is usually classified as a dialect of Northwest Greek, and occasionally as a distinct sister language of Greek or an Aeolic Greek dialect. However, the prestige language of Macedon during the Classical era was Attic Greek, replaced by Koine Greek during the Hellenistic era. Their religious beliefs mirrored those of other Greeks, following the main deities of the Greek pantheon, although the Macedonians continued Archaic burial practices that had ceased in other parts of Greece after the 6th century BC. Aside from the monarchy, the core of Macedonian society was its nobility. Similar to the aristocracy of neighboring Thessaly, their wealth was largely built on herding horses and cattle.