Abstract This study uses treebanking to investigate how spoken language infiltrated legal Latin in early medieval Italy. The documents used are always formulaic, but they also always contain a ‘free’ part where the case in question is described in free prose. This paper uses this difference to measure how ten linguistic features, representative of the evolution that took place between Classical and Late Latin, are distributed between the formulaic and free parts. Some variants are attested equally often in both parts of the documents, while perceptually or conceptually salient variants appear to be preserved in their conservative form mainly in the formulaic parts.