The traditional description of the gaṇacchandas family of metres of Sanskrit and Prakrit literature, of which the āryā metre is the best known, refers to gaṇas or ‘groups’ of mātrās. Mātrās correspond to the ‘moras’ of modern phonology. In this paper the āryā is given a detailed analysis on the basis of the traditional description and the empirical data provided by its use in an early Prakrit anthology, the Sattasaī. Several new metrical phenomena are identified, and the incidence of syllabic patterns, rhythmic structures, word boundaries, and stress are considered. The prosodic foot is shown to play an important role in the regulation of the āryā’s categorical and gradient patterns. This analysis uses Optimality Theory to account for both kinds of patterns and supports recent research that holds partially ranked constraints responsible for gradient patterns in metrical corpora. Other theories, which derive metrical structure by bottom-up rules, fail to account for the āryā’s characteristic patterns.