Francisco Varo's Arte de la Lengua Mandarina (Canton, 1703) is the first Chinese grammar worthy of its name. From the phonological perspective, its significance derives from the fact that it (a) provided the earliest precise formulation of tone sandhi rules in Chinese - at least in a Western language; (b) sought to give plausible phonetic motivations for the pitch changes observed; and (c) offered insightful comments on such topics as underlying vs. surface tones, the function of tonal distinctions and compounding, etc.