On pg. 111 in discussing clitic elements I simply define proclitics as elements that do not receive their own stress, but form a prosodic unit with the following tonic word, but I didn't give any Latin examples or evidence.
It is general thought that a preposition was proclitic on the noun it governed. There are a number of pieces of evidence for this.
First, Quintilian reports (1.5.27) cum dico circum litora, tamquam unum enuntio dissimulata distinctione, itaque tamquam in una voce una est acuta. "For when I say circum litora I pronounce the phrase as one word, concealing the fact that it is composed of two, consequently it contains but one acute accent, as though it were a single word. [translation H. E. Barber, Loeb edition].
Second, we often find prepositions written together with the noun they govern, or, in text which regularly use interpuncts to separate words, with omitted interpuncts. For example, APVRFINEM (ILLRP 7, from Marsian territory), INFRONTE (CIL 12.1319) and with missing interpuncts from the letters of Rustius Barbarus from the Ostraka of Wadi Fawâkhir, 1st or 2nd cent CE: 1.4f. ·per Popilium·, cf. 1.6 ·per Draconem·.
Incidentally the term proclitic, unlike enclitic, does not have ancient roots and was coined by Gottfried Hermann (pictured above) in De emendanda ratione Graecae Grammaticae.
See Adams, J. N. 1996. Interpuncts as evidence for the enclitic character of personal pronouns in Latin. ZPE 111:208–10.