Old Tibetan shows extraordinary complexity in its syllable structure as well as highly complex or rather opaque verb morphology. The syllable structure (CCC)CV(CC) has broken down completely in the modern Central Tibetan dialects to CV(C), while the opaque alternations of prefixes, consonants and vowels in verb stem formation were levelled out and replaced by regular systems of periphrastic construction in the western and central varieties. Both developments can be described as processes of simplification that were triggered in a linguistic contact situation, where Old Tibetan served as a lingua franca for various non-Tibetan peoples.