It is argued that the grammaticalization of these verbs involves an initial stage in which they become equivalent to the copula. Only gradually they expand into the verbal system and become T (ense), A (spect), M (odality) and passive markers. As for the latter function, crucial to the passive interpretation of the sequence fieri/fakere+ past participle is a change in the aspectual nature of the verbs entering the construction, from causative accomplishments to active accomplishments and activities. It is also shown that the rise of these passive verbal periphrases is related to radical changes affecting the domains of voice and grammatical relations, which cut across, at some point in time, the aspectual morphological cleavage existing in the Latin verbal system between imperfective and perfective verbal forms.