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The Greek diacritics were introduced by Aristophanes of Byzantium, which became standard in the Middle Ages. My question is: Is the accent (tone) system of Ancient Greek which we are using now a result of linguistic reconstruction, or it is mainly based on historical references such as the descriptions of ancient grammarians or other sources? The characteristics of different tones might be described by natural language, but how about the position of these accents ? Are there fixed rules to accent words in ancient Greek ?