In the history of European Portuguese, from the 16th to the 19th century, clitic-placement underwent significant changes, specifically with respect to the environments where enclisis obligatorily occurs. In this paper, we show how the architecture of grammar proposed in Distributed Morphology (Embick and Noyer, 2001, 2006) can shed a light on this change. We analyze enclisis as the result of post-syntactic rules and we argue that the change involved a shift in the operation that displaces the clitic from Prosodic Inversion to Lowering, accounting for the different environments where enclisis obligatorily occurs across time. Moreover, the employment of such a view of the architecture of grammar allows us to interpret this shift as a case of grammaticalization, thus broadening the treatment of this concept in the framework of Generative Grammar. (C) 2012 Elsevier B.V. All rights reserved.1228952974