This paper explores the functions of the prepositional phrase consisting of the preposition u 'at' and the genitive with human referent (henceforth indicated as u + GEN) in the history of Russian. In Modern Russian, u + GEN encodes predicative possession, external possessor and the human non-recipient third argument of the verb of 'removing', 'buying' and 'asking/requesting'. Based on the analysis of the Primary Chronicle and the Old East Slavic and the Middle Russian Subcorpora of the Russian National Corpus, the present research aims to demonstrate that the roles of u + GEN should be considered within the Ablative-Locative spread in which u + GEN superseded the locative role and at the same time retained the ablative role. According to the Corpora, u + GEN was already used as a human non-recipient 3rd argument of the mentioned three groups of verbs in Old East Slavic and the entrenchment of this encoding was prominent in Middle Russian. I assume that u + GEN retained its ablative function due to a language-internal drift in the development of the possessive function of the u + GEN and to the influence of language contacts, in which bilingual North Finnic speakers transferred the locative-ablative case syncretism of their mother tongue to Old East Slavic and Middle Russian. 1