Although the order of major sentence constituents at all stages of Ancient Greek is quite free, the distribution of clause types is not random over time, but changes from predominantly verb-final to predominantly verb-medial, suggesting a change in progress. Using the paradigm of Kroch (1989), in which it is assumed that syntactic change involves competition between grammatical systems, two models are constructed, one for the verb-final grammar of the Homeric period (pre-800 B.C.) and one for the verb-medial grammar of the Hellenistic Koiné (c. 100 A.D.). The language of an intermediate stage (Herodotus, c. 450 B.C.) is shown to pattern in part like Homer and in part like the Koiné. More strikingly, the ratio of verb-final to verb-medial structure that best fits the distribution of clause types found in Herodotus is extremely close to an independent measure of this ratio obtained from the distribution of weak pronouns and clitics.