Epigraphy
Macedonian onomastics: the earliest epigraphical documents attesting substantial numbers of Macedonian proper names are the second Athenian alliance decree with Perdiccas II (~417-413 BC), the decree of Kalindoia,~335-300 BC) and seven curse tablets of the 4th c. BC bearing mostly names.
The Pella curse tablet, a text written in a distinct Doric Greek dialect, found in 1986 and dated to between mid to early 4th century BC, has been forwarded as an argument that the ancient Macedonian language was a dialect of North-Western Greek, part of the Doric dialects.
Read more about this topic: Ancient Macedonian Language