Among the numerous representations of the traditional Buddhist biographies of Shakyamuni, the most concise one is that of «twelve great Buddha’s deeds». Its intrinsic logic remained opaque because some crucial facts, e.g. the four numinous encounters, are omitted whereas the worldly pleasures which cannot be considered to be a «deed» at all are mentioned. A structural analysis reveals an un- derlying calendar pattern used symbolically with three types of symmetry which or- ganize this dozen in a whole, viz. 1. Two halves of the year, 2. Similarity an opposition between the items #N and N+6 #N 3. Semantic affinity between the item numbered#X and #Y where X+Y= 13.